RIVERSIDE, Calif. » Rick Ruzzamenti admits to being a tad impulsive. He traded his Catholicism for Buddhism in a revelatory flash. He married a Vietnamese woman he had only just met. And then a year ago, he decided in an instant to donate his left kidney to a stranger.

In February 2011, the desk clerk at Ruzzamenti’s yoga studio told him she had recently donated a kidney to an ailing friend. Ruzzamenti, 44, had never even donated blood, but the story so captivated him that two days later he called Riverside Community Hospital to ask how he might do the same thing.

Halfway across the country, in Joliet, Ill., Donald C. Terry Jr. needed a kidney in the worst way. Since receiving a diagnosis of diabetes-related renal disease in his mid-40s, he had endured the burning and bloating and dismal tedium of dialysis for nearly a year.

"It was like being sentenced to prison," Terry recalled, "like I had done something wrong in my life and this was the outcome."

As a dawn chill broke over Chicago on Dec. 20, Terry received a kidney in a transplant at Loyola University Medical Center. He did not get it from Ruzzamenti, at least not directly, but the two men will forever share a connection: They were the first and last patients in the longest chain of kidney transplants ever constructed, linking 30 people who were willing to give up an organ with 30 who might have died without one.

What made the domino chain of 60 operations possible was the willingness of a good Samaritan, Ruzzamenti, to give the initial kidney, expecting nothing in return. Its momentum was then fueled by a mix of selflessness and self-interest among donors who gave a kidney to a stranger after learning they could not donate to a loved one because of incompatible blood types or antibodies. Their loved ones, in turn, were offered compatible kidneys as part of the exchange.

Chain 124, as it was labeled by the nonprofit National Kidney Registry, required lockstep coordination over four months among 17 hospitals in 11 states. It was born of innovations in computer matching, surgical technique and organ shipping, as well as the determination of a Long Island, N.Y., businessman named Garet Hil.

The chain began with an algorithm and an altruist. Over the months it fractured time and again, suspending the fates of those down the line until Hil could repair the breach. Eventually, he succeeded in finding needle-in-a-haystack matches for patients whose antibodies would have caused them to reject organs from most donors.

Despite an intensely bitter breakup, a Michigan man agreed to donate a kidney for his former girlfriend for the sake of their 2-year-old daughter. A woman from Toronto donated for her fifth cousin from Brooklyn, N.Y., after meeting him by chance in Italy and then staying in touch mostly by text messages.

Children donated for parents, husbands for wives, sisters for brothers. A 26-year-old student from Texas gave a kidney for a 44-year-old uncle in California whom he rarely saw. In San Francisco, a 62-year-old survivor of Stage 4 Hodgkin’s lymphoma donated for her son-in-law.

On Aug. 15, Ruzzamenti’s kidney flew east on a Continental red-eye from Los Angeles to Newark, N.J., and was rushed to Saint Barnabas Medical Center in Livingston, N.J. There it was stitched into the abdomen of a 66-year-old man.

The man’s niece, a 34-year-old nurse, had wanted to give him her kidney, but her Type A blood clashed with his Type O. So in exchange for Ruzzamenti’s gift, she agreed to have her kidney shipped to the University of Wisconsin Hospital in Madison for Brooke R. Kitzman’s transplant. It was Kitzman’s former boyfriend, David Madosh, who agreed to donate a kidney on her behalf despite their acrimonious split.

On and on the chain extended, with kidneys flying from coast to coast, iced down in cardboard boxes equipped with GPS devices and stowed on commercial aircraft.

In a system built on trust, one leap of faith followed another. The most worrisome risk was that donors would renege once their loved ones received kidneys.

After John A. Clark of Sarasota, Fla., got a transplant on Sept. 28 at Tampa General Hospital, his wife, Rebecca, faced a 68-day wait before it was her turn to keep the chain going. Clark said that it crossed her mind to back out, but that she swatted away the temptation.

"I believe in karma," Clark said, "and that would have been some really bad karma. There was somebody out there who needed my kidney."

Many of the 400,000 Americans who are tethered to dialysis dream of a transplant as their pathway back to normal. While about 90,000 people are lined up for kidneys, fewer than 17,000 receive one each year, and about 4,500 die waiting, according to the United Network for Organ Sharing, which maintains the wait list for the government.

Only a third of transplanted kidneys come from living donors, but they are coveted because they typically last longer than cadaver kidneys.

A reason there are not more live kidney donations, however, is that about a third of transplant candidates with a willing donor find that they are immunologically incompatible.

Domino chains, which were first attempted in 2005 at Johns Hopkins, seek to increase the number of people who can be helped by living donors. In 2010, chains and other forms of paired exchanges resulted in 429 transplants.

Garet Hil and his wife, Jan, may never fully recover from the snowy night in February 2007 when they took their 10-year-old daughter in with flu symptoms and emerged with a shocking diagnosis of nephrophthisis, a genetic kidney-wasting disease.

Because Hil and his daughter shared the same blood type, he assumed he would be able to give her one of his kidneys. But two days before surgery, doctors canceled the operations after discovering that his daughter had developed antibodies that would most likely cause rejection.

Fortunately, one of Hil’s nephews then was tested and was able to donate.

After the successful transplant, Hil, a veteran business executive, could not shake his frustration that a more effective registry for paired kidney donation did not exist. "The exchange systems out there weren’t industrial strength," he said.

By the end of 2007, the Hils had formed the National Kidney Registry and rented office space in an old clapboard house in Babylon, N.Y. The couple invested about $300,000 to start it, and Garet Hil, who is now 49, ran the registry without a salary.

Hil marketed his registry to hospitals with PowerPoints and passion. The transplant world initially regarded him as an interloper. But he has now persuaded 58 of the country’s 236 kidney transplant centers, including many of the largest, to feed his database with information about pairs of transplant candidates and their incompatible donors.

In 2007, a transplant surgeon at the University of Toledo Medical Center, Dr. Michael A. Rees, had a forehead-slapping insight. If an exchange began with a good Samaritan who donated to a stranger, and if the operations did not have to be simultaneous, a chain could theoretically keep growing, limited only by the pool of available donors and recipients. Rees reported in 2009 that he had strung together a chain of 10 transplants.

Hil seized on the idea and set out to build an algorithm that would enable even more transplants

Nowadays, Hil’s pool typically consists of 200 to 350 donor-recipient pairs. That is enough to generate roughly a googol — 10 to the 100th power — of possible chains of up to 20 transplants if all of the pairs are compatible, said Rich Marta, the registry’s senior software designer.

There are several registries like Hil’s, each with a distinct approach. Largely unregulated by government, they invite sensitive questions about oversight and ethics, including how kidneys are allocated. A number of medical societies are convening in March to seek consensus on that and other issues related to paired exchanges.

Long transplant chains save more lives than short chains. But they come with trade-offs because the longer they grow, the higher the risk that a donor will renege or that a link will break for other reasons.

The dependency of each link on the others kept patients on edge. "Things can happen," Candice Ryan fretted a few days before her Dec. 5 transplant at Massachusetts General Hospital. "You just pray that everything goes well. I can’t relax until I’m asleep and on the table."

Until recently, hospitals regularly turned away good Samaritan donors on the working assumption that they were unstable. That has changed somewhat with experience. But when Rick Ruzzamenti showed up at Riverside Community Hospital asking to give a kidney to anyone in need, he still underwent rounds of psychological screening as well as medical tests.

The doctors and social workers did not know what to make of Ruzzamenti at first. He had a flat affect and an arid wit, and did not open up right away. As the hospital’s transplant coordinator, Shannon White, pressed him about his motivations and expectations, he explained that his decision seemed rather obvious.

"People think it’s so odd that I’m donating a kidney," Ruzzamenti told her. "I think it’s so odd that they think it’s so odd."

The hospital wanted to make sure that he was not expecting glory, or even gratitude. Ruzzamenti stressed that no one should mistake him for a saint.

By Dec. 19, Chain 124 hurtled toward its conclusion with a final flurry of procedures at Ronald Reagan UCLA Medical Center in Los Angeles. Between dawn and dusk, three kidneys were removed and three were transplanted in neighboring operating rooms. One flew in from San Francisco. The last took off for O’Hare.

At the end of the cluster were Keith Zimmerman, 53, a bearish, good-humored man with a billy-goat’s beard, and his older sister, Sherry Gluchowski, 59. She had recently moved from California to Texas but returned to donate her kidney.

Gluchowski’s kidney went to Loyola University Medical Center in Chicago to be transplanted into Terry, the last in the chain.

Chain 124 ended at Loyola because Hil had arranged the final kidney to go to a hospital that had produced a good Samaritan donor to start a chain in the past, thus closing a loop. Dr. John Milner, a transplant surgeon at Loyola, said he then selected Terry to receive the kidney because he was the best immunological match on the hospital’s wait list.

When Milner called with the news in early December, Terry was floored at his remarkable good fortune.

As it sank in that his would be the last of 30 interconnected transplants, Terry began to feel guilty that he would be ending the chain. "Is it going to continue?" he asked Milner. "I don’t want to be the reason to stop anything."

"No, no, no," the doctor reassured him. "This chain ends, but another one begins."

© 2012 The New York Times Company