A high incidence of osteopenia is likely in renal transplant recipients in whom pre-existing uraemic osteodystrophy, persisting hyperparathyroidism and glucocorticoids constitute a formidable array of risk factors. The correction of some biochemical and hormonal abnormalities, an increase in body weight and an increase in physical activity following transplantation could favour improvements in skeletal integrity. Using dual energy X-ray absorptiometry (DEXA), we studied prospectively the regional bone mineral density (BMD) of 34 consecutive cadaveric renal allograft recipients who were already established on dialysis. BMD of these patients was measured at the time of transplantation and was repeated at 3, 6 and 12 months following the transplantation. Immunosuppression was achieved using triple therapy: azathioprine, cyclosporin-A and prednisolone. At baseline, total BMD and BMD at the lumbar spine and femoral neck did not differ from age- and sex-matched controls. Females experienced marked and progressive bone loss at the lumbar spine, with less marked changes at the femoral neck. Males, in contrast, experienced substantial reduction of BMD at the femoral neck at 6 months and a recovery at 12 months without significant change at the lumbar spine. Whole body bone mineral content fell transiently in males, with partial recovery by 6 months. No significant correlation was found with the cumulative doses of either corticosteroids or cyclosporin-A, the duration of hospitalisation, the function of the transplant, patient age or menopausal status. In females the loss of BMD at the lumbar spine at 6 months was closely associated with a high parathyroid hormone level (PTH) at transplantation, and in males, the loss of BMD at the femoral neck was associated with a low PTH level at transplantation. We conclude that rapid falls in BMD appear to be inherent to the process of renal transplantation and that strategies to prevent this loss should be evaluated.