For Robert McFall, 39, of Pittsburgh, the nightmare began in June with bruises that wouldn't heal and nosebleeds that wouldn't stop. When he went to the hospital, doctors told him he was suffering from a severe blood disease, aplastic anemia. Unless he received an immediate bone marrow transplant, they said, he was virtually certain to die—and the chances of finding a suitable donor were slim, perhaps 60,000 to 1. McFall's six brothers and sisters all failed tests for compatibility before his cousin, David Shimp, 43, surprisingly proved a perfect match. Then the unthinkable happened: Shimp refused to go through with the transplant. "He came up to my room after the blood test," McFall remembers, "and put his arm around me and told me in a very friendly way he wasn't going to donate the marrow. He said he had a dream he'd go into the hospital and not come out."

Neither McFall nor other family members were ready to accept Shimp's decision. Doctors tried to assure him that the procedure, involving about 150 extractions from his pelvic bone, is all but painless for the donor. McFall's relatives implored him to do it for humanitarian, if not family, reasons. But Shimp remained adamant and his wife, Sharon, reportedly threatened to leave him if he changed his mind. Finally McFall took his cousin to court. Judge John P. Flaherty Jr. found Shimp's position "morally indefensible," but ruled that he could not be forced to submit to the procedure. "I understand why the judge did what he did," said McFall's sister Beverly. "I'm just sorry that the legal and moral laws in our country aren't harmonious. There's some deep secret in that Shimp family and because of it we've suffered terribly for many years."

Shimp tantalizingly agrees. "There is a story behind all this," he says, "and I will reveal it in the near future." McFall theorizes that he and his cousin may in fact be half brothers. "I've heard that my mother might have been raped by David's father," says McFall matter-of-factly. "David and I have kind of talked about it before, without really talking about it." That might explain Shimp's compatibility as a donor, which doctors say is relatively rare between cousins.

Whatever the reason for all the bad blood, the latest acrimony has driven the two families into an escalating war of words—and alienated Shimp from his own relatives. "I can't believe he's just going to stand there and let Bobbie die," says Shimp's 14-year-old daughter by his first marriage. "At first I felt bad for my father, but my mind has changed completely." Says ex-wife Mildred: "During all the time of our marriage David was always a hypochondriac. But he's a very healthy man."

As young men together in Pittsburgh, Shimp and McFall, who had been placed in an orphanage at 10, seemed more like the brothers they were rumored to be than the strangers they have become. "I used to help him work on his house," McFall says fondly, "and we went camping a couple of times. Our relationship was damn good. We'd go out for some beers now and then and raise hell. Why, I remember when I gave him money to put food on the table and bought toys for his kids. I'm a Christian cousin." But Shimp's mother, Ruth, 65, has curiously uncharitable memories of her nephew. "Robbie was always a very engaging person," she says bitterly, "but now I have no sympathy for him. He's never had any responsibilities. He never got married—David has a new wife and family to think about. David's wife was threatened the other day. Someone called and said, 'If Robert McFall dies, you die.' Those McFalls are vipers. Robbie's lying there so pitifully—I'd like to take out a violin and play Hearts and Flowers."

The prognosis for McFall is grim. Death could come at any time, say doctors, through either infection or a sudden massive hemorrhage. Meanwhile he is being kept alive with blood transfusions and hormone pills. "There are days when it feels like my heart's on top of my head," says McFall. "There's a throbbing. And I break out with something like measles on my legs." One result of McFall's much-publicized ordeal is a reunion with some of his brothers and sisters whom he had not heard from since their mother died in 1949. The person he would most like to see, of course, is David Shimp, but a change of heart seems unlikely. "We all have to meet our Maker sometime," says Shimp. "Who is he to ask me to give up parts of my body?" McFall can only keep hoping. "I feel sorry for David," he says, "but I bear him no grudge. He has to live with this thing."