Background: Loss of bone mass is usually detected after bone marrow transplantation (BMT), especially during the early post-transplant period. But little is known about the long-term effects of BMT on bone mineral metabolism. Methods: We have investigated prospectively 12 patients undergoing BMT (4 autologous, 8 allogeneic) for hematologic diseases (8 leukemia, 3 SAA, 1 MDS). Serum concentrations of calcium, phosphorus, creatinine, gonadotropins, sex hormones and bone turnover markers (osteocalcin and ICTP) were measured. The samples were collected before BMT and 1, 2, 3, 4, and 12 weeks, 6 months and 1, 2 years thereafter. Bone mineral density (BMD) was measured with DEXA (Dual Energy X-ray Absorptiometry) before BMT, 1 year and 2 year after BMT. In patients with amenorrbea, hormone replacement therapy was started from around 1 year after BMT Results: 1. The mean bone loss in the lumbar spine, calculated as the percent change from the baseline to the level at 1 year and 2 year was 7.3% and 1.9%, respectively. The mean bone loss in the total proximal femur from the baseline to the level at 1 year and 2 year was 8.0% and 8.3% respectively. 2. The serum ICTP increased progressively until four weeks after BMT. Thereafter, it decreased gradually to reach basal values after one year and thereafter no more change until 2 year. Serum osteocalcin decreased progressively until three weeks after BMT. After that, it increased and reached basal values after 3 months. Osteocalcin increased at 6 month transiently but thereafter, it decreased to the level of slightly above basal value at 2 year. 3. Patients who were treated with TBI or pateints with GVHD had a tendency of lower BMD at l year and 2 year after BMT than those of patients without TBI or GVHD. 4. Eight out of nine women went into a menopausal state immediately after BMT and remained amenorrhea, evidenced by high gonadotropins and low estradiol levels. In contrast to women, gonadotropins and testosterone levels were not changed significantly in men after BMT. Conclusion: The rapid impairment of bone formation and the increase in bone resorption, as shown by the biochemical markers in this study, might play a role in bone loss after BMT. The efficacy of HRT for the correction of hypogonadism and bone loss was evidenced by 2 year BMD which was much more increased compared to 1 year BMD, especially in vertebra (J Kor Soc Endocrinol 15:561-570, 2000).