Seventy-four responses were received from a questionnaire which had been mailed to 91 bone marrow transplantation institutes throughout Japan to assess the activity of bone marrow transplantation and complications in bone marrow donors. A total of 2329 bone marrow harvests, performed from 1688 adult donors and 641 child donors for allogeneic or syngeneic transplantation up to August 1992, were available for study. Analyses of the responses showed slight diversity regarding the marrow harvesting preparation and methods of the different bone marrow programs. The resulting perioperative complications were principally caused by anesthesia: 73 episodes of hypotension including one death 18 months later, seven of arrhythmia, one of respiratory arrest, three of mental confusion, one of asthma, one of malignant hyperthermia, one tooth injury and one broken aspiration needle. The postoperative complications were chiefly caused by marrow aspiration per se: 731 episodes of transient fever, 26 of long-lasting pain or discomfort, 10 episodes of liver dysfunction including two cases of non-A, non-B hepatitis, four cases of infection, one episode of hypotension, one of dysuria and one case of keloid formation. The study further revealed that the frequency of complications was lower in child donors than in adult donors.