The accident occurred in late February on a cold Moscow street. A 16-year-old boy, with fatal head injuries, was taken to the Institute of Transplantation, a medical complex set in a birch forest on the outskirts of the city. Dr. Valery I. Shumakov, head of the institute, made the decision. He and other surgeons opened the torso and removed the dead boy's kidneys. One was transplanted immediately into Georgi Dudayev, 41, a resident of the Soviet Republic of Georgia. The other kidney was packed in a sterile solution, wrapped in plastic bags, surrounded by ice and rushed to Moscow's Sheremetyevo airport for the nonstop Aeroflot jet to New York. Shumakov telephoned the American doctors that the kidney was on the way.

Thus began a dramatic and unprecedented experiment in U.S.-Soviet medical cooperation, a detente among doctors. Before it was over, two stricken men would lead normal lives again, and the world would glimpse the monumental benefits possible when the superpowers work together.

An ambulance was waiting at Kennedy airport. The kidney was brought to New York Hospital, where the donor's blood and tissue samples were compared with those of more than 200 patients waiting for transplants. The doctors' choice was a Brooklyn construction worker named Jose Serrano, 32. His body seemed most likely to tolerate the kidney from Moscow.

Last October Serrano's own kidneys failed, and to stay alive he was put on dialysis three days a week, four hours each time. "We were losing hope," Serrano's wife, Louisa, said, "because kidneys are rare, and many people are on the list." When Jose was summoned to the hospital for the operation, Louisa had an attack of nerves, and her ailing husband had to drive the car.

Less than 48 hours after the kidney was removed in Moscow, it was implanted in Serrano. (His own nonfunctioning organs were left in place because they continue to produce a needed hormone.) Within 12 hours after surgery, the new kidney had produced more than five quarts of urine and was functioning well. Although Serrano had to be hospitalized a second time for minor post-surgery complications, his health was improving, he was able once again to eat the specialties of his native Puerto Rico (like red beans and fried bananas), and he looked forward to working again.

Medical cooperation between the Soviet Union and the U.S. commenced with a treaty signed in 1972. In the area of organ transplants, two prime movers have been Shumakov and Dr. Albert Rubin, director of the Rogosin Kidney Center at New York Hospital. The collaboration has also included joint experiments with an artificial heart. "The Americans have better plastic materials for the heart pump itself," says Shumakov, "and we have good systems for automatic controls."

Shumakov, 45, is Russia's most experienced transplant surgeon, having performed some 250 such operations. In January he implanted an artificial pancreas, a Soviet breakthrough, and he and his staff have been conducting experiments on the feasibility of liver transplants.

A burly man built like a weightlifter (6'2", 230 lbs.), Shumakov once played volleyball and threw the discus but now has little time for anything but work. In his off-hours, he is grateful for a quiet evening at home with his wife, Natalie, who is an anesthesiologist, and their two children, Olga, 13, and Dimitri, 10.

In the Soviet Union, as in this country, the number of transplant operations is limited essentially by a shortage of donors. (In the U.S., as many as 10,000 patients may be awaiting kidney transplants; less than one third that number got kidneys last year.) Shumakov is particularly keen on continued Soviet-U.S. cooperation in this area. "An exchange of kidneys," says Shumakov wryly, "seems to me more practical and tangible than an exchange of delegations. The more donors we have, the better the chance to get compatible organs and patients." (The U.S.S.R. also has somewhat fewer legal obstacles than the U.S. in obtaining organs for transplant.)

With present technology, the doctors in Moscow and New York had a maximum of 72 hours to transplant the Russian kidney. "We didn't pick Serrano because he was a Brooklyn construction worker," explains Dr. William Stubenbord, 40, who performed the operation at the kidney center in New York. "We do not make decisions for socioeconomic reasons. A kidney is a kidney no matter where it comes from." He points out that the success rate where donor and receiver are unrelated runs between 40 and 50 percent. In cases of relatives, the odds increase to as much as 90 percent.

The Russian Dudayev, who received the first kidney, has been allowed to go home to Soviet Georgia. Serrano hopes to return to Puerto Rico with his wife and children when he is fully recovered. "I want to talk to families with kidney problems," he says. "They're scared." Although doctors say Serrano could probably return to construction work, he seems to want to learn a new vocation. Meanwhile, the family lives on Social Security and unemployment payments to which transplant patients are entitled.

Not long ago, Serrano met Dr. Shumakov for the first time and to his credit voiced an appeal for his friends still suffering through dialysis. "Thanks," the boyish Puerto Rican said, "and please try to send more."