A man who donated one of his kidneys to save his mother's life seven years ago died hours before she could repay him with a bone marrow transplant to help him overcome leukemia, authorities said Monday. ``I'm really heartbroken,'' Ernestine Mitchell said. ``If only he could have lasted eight more hours.'' Her 37-year-old son, Hilliary, had been unable to work as a truck driver since contracting leukemia, and was to receive the bone marrow transplant during a day-long operation beginning at 7:30 a.m. He died of an infection shortly before midnight Sunday, said John Easton, spokesman for the University of Chicago Hospitals. Mitchell died from ``an overwhelming infection related to the leukemia and the loss of his immune system,'' Easton said. ``High doses of chemotherapy needed to combat the disease and prepare the patient for the transplant can leave the patient without a functioning immune system.'' Mrs. Mitchell said she and other family members were at her son's bedside Sunday and had expected him to hang on for the potentially life-saving procedure. ``It's a hurting thing, but I have to remain strong because he was strong at the end,'' Mrs. Mitchell said. ``He talked to us and was kissing us all and we thought he was getting better. We were waiting for 7:30 to come.'' Mrs. Mitchell said she was convinced her bone marrow would have helped. ``I carried him for nine months, his body was a part of my body. Then he gave me his kidney,'' she said. ``I know that if he had gotten the marrow everything would have been OK. Being a mother, I think it would have.'' Mitchell himself knew that his odds were not good because his disease was already at an advanced stage and he had been hospitalized before because of other infections, Easton said. Leukemia is a form of cancer in which abnormal cells can spread in the bone marrow, preventing it from making normal blood cells. This leaves the patient highly susceptible to serious infections, anemia and bleeding. A transplant replaces the patient's defective marrow with healthy marrow. Easton said the mother's bone marrow removal operation had been scheduled for this morning, with the transplant to be done in the afternoon. The operation was filled with risks, and the odds of Mitchell's recovery were 25 percent to 40 percent, he said. Mitchell had been mentally prepared, said Dr. Robert Geller, who was to have performed the transplant. ``When you've got no options, you go with what you've got,'' Geller said. Mitchell already had won one battle in getting the money for the $150,000 transplant from the state Medicaid program after Gov. James R. Thompson stepped in and reversed a decision denying funds for the operation. ``Getting the money was the hard part,'' Mitchell said as he entered the hospital March 23. ``I'm a survivor. I've walked in here and I'm going to walk out again, well.'' Geller, a bone cancer specialist, said Mitchell had been under intensive chemotherapy for the past 10 days. Those drugs and the anti-rejection drugs Mitchell would have received are highly toxic, ``and the kidney is the most important organ in handling that toxicity.'' He said Mitchell's leukemia was in an aggressive phase and that his mother was not an ideal donor. Perfect bone marrow tissue comes from a brother or sister with an identical tissue match, Geller said. But Geller said tissue match between mother and son had been good enough in the kidney operation. Mrs. Mitchell had been dying of polycystic kidney disease. Her son's act in donating his kidney ``is more dear to me now than ever,'' Mrs. Mitchell said. ``I have an everlasting part of him, my perpetual Mother's Day gift.''