Renal function was determined before and at varying times after chemotherapy in 62 patients with metastatic germ cell tumours treated with carboplatin. Eighteen patients were excluded because of urinary tract obstruction, leaving 44 evaluable patients treated with carboplatin either as a single agent (13 patients) or in combination with other agents (31 patients). No significant differences were observed in mean 51Cr-labelled Ethylenediamine tetraacetic acid (EDTA) clearances before and after carboplatin in either the group as a whole (P = 0.58), or when assessment at 1 month or less (P = 0.4), 3 months or less (P = 0.91), or later than 3 months (P = 0.38) were analysed. Carboplatin does not have significant renal toxicity when used at conventional dosage in patients with germ cell tumours.