Of 53 patients with Stage II seminoma treated with radiotherapy between 1970 and 1984, 9 (17%) relapsed, 5 (9%) died of testicular cancer and 1 (2%) died of intercurrent disease. Relapse rates for IIA, IIB and IIC were 11, 18 and 28% respectively. Supradiaphragmatic irradiation was not advantageous; of 22 patients receiving infradiaphragmatic irradiation, 3 (14%) relapsed, compared with 6/31 (19%) of those who had supra- and infradiaphragmatic irradiation. Despite the radioresponsiveness of seminoma, 50% of IIC patients had residual masses 4 months after radiotherapy and 20% at one year, however, this finding did not predict eventual outcome. Serum human chorionic gonadotrophin (HCG) levels were raised prior to radiotherapy in 3/26 (11.5%) Stage IIA and IIB patients and 3/10 (30%) IIC patients. However, this did not influence the outcome of radiotherapy since only 0/6 patients with raised HCG levels relapsed compared with 7/30 (23%) of those with normal levels. Analysis of the pattern of relapse together with the fact that 2/6 patients who had the extent of tumour defined at laparotomy and/or who had total abdominal irradiation relapsed, suggests that further refinement of radiotherapy is unlikely to improve the results of treatment for IIC patients and that chemotherapy should be considered the treatment of choice.