On the assumption that hemodynamic changes in renal blood flow are the initial expression of cis-diamminedichloroplatinum (CDDP)-related nephrotoxicity, we treated patients with metastatic non-seminomatous testicular carcinoma during CDDP infusion with captopril. This angiotensin-converting enzyme inhibitor significantly attenuated the initial decrease in effective renal plasma flow and can probably be used to protect the kidneys against CDDP-induced nephrotoxicity.