Renal function studies were performed in 18 patients with nonseminomatous testicular cancer during four platinum-containing chemotherapy courses. The first 9 patients received chemotherapy alone, the second 9 also captopril, an angiotensin I converting enzyme inhibitor, in order to prevent cis-diamminedichloroplatinum-induced nephrotoxicity. In the first group a decrease in glomerular filtration rate, that was preceded by a fall in effective renal plasma flow, was observed. In the second group, captopril was able to prevent the initial decrease in effective renal plasma flow, but failed to prevent the ultimate decrease in glomerular filtration rate.