The human germ-cell tumour cell line GCT 27 growing as subcutaneous xenograft tumours in male nude mice was used in the 4th and 5th passage to study chemotherapeutic drug responses. Recipient mice received 5 Gy whole body irradiation immediately before tumour transplantation. The median take rate was 62% (range 39-73%) and the median volume doubling time 14 days (range 7-28 days). For bleomycin, cisplatin and carboplatin a clear dose response for growth delay was observed. Bleomycin caused substantial weight loss at doses above 75 mg/kg whereas good response to cisplatin was obtained without serious toxic effects. Vinblastine and etoposide exerted no effect when given in non-toxic doses. The response to etoposide was not improved either by fractionated treatment or by combination with verapamil. However, the combination of 20 mg/kg etoposide and 2 mg/kg cisplatin, which when given alone were ineffective, led to a growth delay that was equal to that observed following the administration of higher cisplatin doses. This effect may be explained by the fact that etoposide, as an inhibitor of DNA-topoisomerase II, may interfere with the repair of DNA interstrand cross-links caused by cisplatin.