Forty-one patients with advanced non-seminoma germ cell testicular tumours were treated by chemotherapy, with or without radiotherapy, followed by excision of residual para-aortic lymph node masses. All para-aortic metastases were initially greater than 2 cm, 35 were larger than 5 cm, and 9 were over 10 cm in diameter. Seven patients also had nodal deposits above the diaphragm and 18 had distant metastases. The residual masses were excised completely in all except 3 cases. Residual malignancy was found in 7 (18%) of 38 operable cases; of these 7, only 2 remain alive and disease-free. In contrast, 28 (90%) of 31 operable cases with necrosis and fibrosis, or with fully differentiated teratoma, are alive and disease-free. Elevated serum markers were found in 6 of 9 cases with resectable or unresectable residual malignancy, but in only 1 of 32 who were tumour-free. Residual malignancy was found in 3 (9%) of 34 cases with normal marker levels. Malignancy was not found in any residual mass less than 4 cm diameter. We conclude that excision of para-aortic lymph node masses should be electively delayed until serum markers become normal and until shrinkage of the mass has ceased. The presence of residual malignancy in the excised tissue then provides a clear indication for further chemotherapy.