To investigate the effect of cyclosporine A (Cyc A) on the development of fibroadenomas, 30 renal transplant patients and 20 chronic renal failure patients on dialysis were breast examined with ultrasonography and/or mammography. Of the renal transplant patients, 17 were receiving Cyc A-based combination therapy for immunosuppression. All patients were female with the age range of 29.7 +/- 9.2 years in the transplant group and 33.95 +/- 9.91 in the dialysis group. Eight of the 17 patients receiving Cyc A had fibroadenomas, 5 of them having bilateral lesions. None of the other patients, those on dialysis and on non-Cyc A combination therapy had fibroadenomas. A significant difference for fibroadenoma incidence in patients receiving Cyc A combination immunosuppression was found.