The effect of alfacalcidol therapy on bone mineral density at the spine and proximal femur was evaluated in 112 transplant recipients (59 heart, 26 liver and 27 lung); 45 transplant cases served as controls (included in a randomised way in a placebo group) and in 42 rheumatoid arthritis cases. Liver and lung transplantation cases had before transplantation a lower bone density at the spine and femur compared to heart transplant cases. Heart transplant cases lost considerably more bone immediately after transplantation than liver and lung transplant recipients. A positive effect of 2 years alfacalcidol treatment (0.5-1 microgram/day) on bone loss was observed in all treated groups. Alfacalcidol was particularly effective against trabecular bone loss at the spine in rheumatoid arthritis patients and transplant recipients. There is a manifest difference in evolution between organ transplant groups and bone sites measured. Liver and lung transplant recipients respond better to therapy than cardiac recipients.