We evaluated metacarpal index (MCI) and bone mineral content (BMC) of right 2nd metacarpal bone X-ray films using the microdensitometer technique in 12 pediatric and 32 adult renal transplant (Tx) recipients. Grafts were well functioning for more than 1 year in all adults (serum creatinine ≤ 2, 0 mg/dl) and in 9 of the children (serum creatinine≤ 1, 2mg/ dl). Immunosupression consisted of cyclosporin (CyA), methylprednisolone (MPL), mizoribineand anti-lymphocyte globulin for all children. 18 of the adults were given CyA and 14 were given conventional immunosupression. BMC was found to be increased in both children with good renal function and in adults. MCI was improved in 2 children with good renal function and in 2 adults using CyA. Immunosupression of CyA and low dose MPL had an improving effect on renal osteodystrophy. Alternate-day MPL dosage was between 1, 6 and 7.3 mg/m2 day (mean 3, 6 mg/m2/day) in the 9 children with good renal function. Bone age of the children was seen to be developed in accordance with calender age. Growth velocity of the 9children with good renal function was better than the mean level of normal children. However, growth velocity at 3 years after Tx declined slightly, compared with that within 2 years. Similarly, somatomedin C was above the normal range within 2 years after Tx. Thus, bone metabolism after Tx may have been influenced by serial changes of somatomedin C.