When Alberty Jose da Silva heard he could make money, lots of money, by selling his kidney, it seemed to him the opportunity of a lifetime. For a desperately ill 48-year-old woman in Brooklyn whose doctors had told her to get a kidney any way she could, it was.

At 38, Mr. da Silva, one of 23 children of a prostitute, lives in a slum near the airport here, in a flimsy two-room shack he shares with a sister and nine other people. "As a child, I can remember seven of us sharing a single egg, or living for day after day on just a bit of manioc meal with salt," Mr. da Silva said in an interview.

He recalled his mother as a woman who "sold her flesh" to survive. Last year he decided that he would, too. Now, a long scar across his side marks the place where a kidney and a rib were removed in exchange for $6 000, paid by middlemen in an international organ trafficking ring.

Among poor men like Mr. da Silva and others who have migrated to slums here from Brazil's parched northeastern backlands, word of the market to sell their organs spread quickly. Some who had done so were already buying houses, businesses, cars and refrigerators. The sums being offered seemed a fortune. The minimum wage here is barely $80 a month, and work is hard to find. Many men struggle to exist on odd jobs that pay barely a dollar a day. Initially, the organ brokers paid as much as $10 000 for a kidney—more than a decade's wages.

Donors and recipients were not related, in contrast to the usual preference for legal and medical reasons. In fact, they did not even know each other. But they were linked by a trafficking ring that the authorities now say exploited two very different sets of needs—for money and for life itself—at opposite ends of a tangled chain thousands of miles long.

Tracing the journey of Mr. da Silva's kidney through that chain, which spanned four continents and ended in a one-bedroom apartment in Brooklyn, reveals the inner workings of a network that human rights groups say is by no means unique. Rather, they say, it is representative of a global black market for organs, including livers, kidneys and lungs, that touches dozens of countries and generates many millions of dollars a year.

In Alberty da Silva's case, the authorities here say, the organ's odyssey began with two middlemen based in this gritty port city of 1.5 million people: Gedalya Tauber, a former Israeli police officer, and his partner, Ivan Bonifacio da Silva, a retired Brazilian military police officer. The pair, since jailed on organ trafficking charges, not only handed out cash payments, the authorities say, but also arranged for the medical exams to weed out unqualified donors. They then obtained passports and airline tickets for the donors to travel to South Africa, where the transplants took place. Both countries have laws against commercial trade in organs.

"Six grand is a lot of money, especially when you don't have any," Mr. da Silva said when asked why he had given up his kidney. "No one here warned us that what we were doing was illegal." It is illegal in the United States to pay a donor for an organ. But Nancy Scheper-Hughes of Organs Watch, a human rights group in Berkeley, Calif., that has long tracked the illegal organ trade and denounced abuses, says irregularities still occur.