Three hundred thirty-two marrow graft recipients and 241 healthy marrow donors were studied by skin testing with recall and neoantigens. Two hundred thirty patients with leukemia and seventy-eight patients with aplastic anemia received allogeneic HLA-identical sibling marrow. Twenty-four patients with leukemia received syngeneic marrow. The conditioning regimen prior to marrow infusion consisted of 120 mg/kg cyclophosphamide and 9.2-15.75 Gy total-body irradiation (leukemia) or 200 mg/kg cyclophosphamide (aplastic anemia). The patients were skin-tested with the neoantigens dinitrochlorobenzene (DNCB), keyhole limpet hemocyanin, and a battery of five recall antigens around 100, 150, 365, 730, 1095, 1460, and 1825 days after grafting. A binary logistic regression analysis was used to investigate the factors thought to influence immunocompetence. At 3 months postgrafting, the proportion of patients positive to DNCB was equal to that of normal marrow donors, but thereafter it was lower until 2 years. The proportion of patients positive to keyhole limpet hemocyanin was lower than normal regardless of the time after grafting. The proportion of patients positive to recall antigens was lower than that of normal marrow donors until 4 years after grafting. Patients with a history of acute graft-versus-host disease had the lowest probability of a positive reaction to recall antigens. None of the other factors was significantly associated with an increased or reduced level of response.