The long-term effect of cisplatin on renal function was studied in a follow-up investigation, 16 to 52 months after chemotherapy in 22 patients with disseminated nonseminomatous testicular cancer. The median cumulated cisplatin dose was 452 mg/m2 (range, 275-650 mg/m2). Prehydration with isotonic saline secured diuresis above 100 ml/hour. GFR (glomerular filtration rate: 51Cr-EDTA clearance) fell by 12.5% (median, P less than 0.01) compared with the pretreatment level. Effective renal plasma flow (125I-hippuran clearance) was estimated to be likewise reduced. The serum creatinine level rose 8 mumol/1 (median, P less than 0.05) during the treatment period with no further rise afterwards. Serum magnesium and urinary excretion of beta-2-microglobulin were normal. The results indicate a moderate and permanent reduction in GFR with no signs of long-term tubular defects in patients treated with cisplatin.