The renal function was evaluated with 131I-Hippuran clearance in 171 patients with malignant germ cell tumours. Assessments were performed before treatment and at three fixed times afterwards within 5 years. The patients were treated with surgery only (20 patients), infra-diaphragmatic radiotherapy only (median midplane dose 36 Gy) (48 patients), cisplatin-based chemotherapy (total cisplatin dose 500-850 mg) plus surgery (64 patients), cisplatin-based chemotherapy (total cisplatin dose greater than 850 mg) with or without surgery (23 patients) or cisplatin-based chemotherapy (total cisplatin dose 500-850 mg) plus infra-diaphragmatic radiotherapy (16 patients). No renal impairment was observed for patients treated with surgery only. In patients who received radiotherapy no change of the renal function occurred during the first year post-treatment. Three to five years after treatment discontinuation a statistically significant reduction within the normal range was observed in patients who were greater than 40 years at the time of irradiation. Cisplatin-based chemotherapy led to a statistically significant irreversible renal impairment for all the three groups. The greatest reduction was seen in patients who received the highest total cisplatin dose or who were treated with irradiation in addition to chemotherapy. The clinical significance of the observed nephrotoxicity is still unknown.