We do not know whether this abnormal growth of B-lymphocytes were malignant or not," Dr. Shearer said, raising the possibility that cancer may have played a role in his death.

David's deteriorating condition had at first been tentatively ascribed to a condition called graft versus host disease, a condition in which transplanted cells in essence attack those of the host body. Results of Autopsy

But an autopsy showed that apparently was not the case.

"David's death was as amazing as his life," Dr. Shearer said. "The finding was totally a surprise to us."

Moreover, the doctor said, it was of extraordinary significance. "David's life was important," he said, "but his greatest contribution medically washis death, because with this information, we will be able to treat other children with this disease." He did not elaborate.

Beyond that legacy, David somehow managed through it all to cheer those around him. "He was ready for problems," Dr. Shearer said. "But he tended to hide his feelings. Whatever the situation was in the last few days, he made it easy for the doctors."

As he fell increasingly ill, David developed difficulty breathing, and the decision was made to put him in artificial respiration, aided by sedation.

"I always told David what we were going to do," Dr. Shearer said, "and I told him I was going to breathe for him and that in order to do that I was going to give him something that was going to make him very sleepy. He agreed with that and he winked at me. That was the last indication." A Calculated Risk