Background. Osteoporosis has been recognized as an important side effect of long-term and of pulsed steroid application after heart transplantation. Methods. In June 1989 a prospective clinical trial was started to study bone demineralization by quantitative computed tomographic scan. All patients received vitamin D and calcium. In group I (n = 30) synthetic calcitonin (40 Medical Research Council Standard Units subcutaneously per day was administered in 14-day cycles, whereas group II patients (n = 31) received a placebo preparation. Repeat trabecular and cortical quantitative computed tomographic scans of the thoracic (T12) and lumbar spine (L1, L2, L3) were obtained within 48 weeks after heart transplantation. Results. Expressed as the means of T12, L1, L2, and L3, trabecular bone density decreased significantly from 100 +/- 24 to 79 +/- 29 mg/mL within 3 weeks after heart transplantation, followed by a further reduction to 67 +/- 29 mg/mL after 3 months in the calcitonin group. The values for cortical bone density decreased significantly from 229 +/- 37 to 202 +/- 40 mg/mL (calcitonin) 3 weeks after heart transplantation. Comparable results were obtained in the placebo group. In both groups bone density remained stable thereafter. Intergroup differences were not of statistical significance. Conclusions. In heart transplant recipients progressive trabecular bone demineralization is limited to the first 3 postoperative months. Thereafter, bone density remained stable. A positive effect of synthetic calcitonin in addition to prophylactic calcium and vitamin D application could not be proved by repeat quantitative computed tomography. (C) 1999 by The Society of Thoracic Surgeons.