Nine patients (Group A) with histologically proven, nonseminomatous testicular cancer were treated with cisplatin (CDDP) according to the Einhorn regimen. Renal function studies including the measurement of the effective renal plasma flow (ERPF) and the glomerular filtration rate (GFR) were performed prior to the chemotherapy and then after treatment on days 10 and 21 of the first course. In order to prevent CDDP-induced nephrotoxicity, verapamil (a calcium entry blocker) and cimetidine were given along with CDDP. The results were compared with others from another group of nine patients (Group B) treated with CDDP, but without verapamil and cimetidine. In Group A there was much less of a decrease in ERPF as compared to Group B on day 21. In addition, the decrease in GFR on days 10 and 21 was totally prevented in the verapamil- and cimetidine-treated group.