Pure testicular seminoma has historically been treated primarily with radiation therapy, and excellent results have been achieved. Recently, several aspects of the treatment of seminoma have been questioned; namely, the value of mediastinal irradiation in Stage II disease, and whether a dose response curve existed for seminoma. Because these questions have remained unanswered, we undertook a retrospective review of all patients with pure testicular seminoma treated in the Department of Radiation Oncology at Indiana University Medical Center. From 1961-1981, 54 patients with pure testicular seminoma were given megavoltage irradiation with curative intent. Thirty three patients were Stage I, with tumor confined to the testicle with no evidence of nodal spread. Fifteen patients were Stage IIA, with metastases less than 5 cm in size in the retroperitoneal nodes. Four patients were Stage IIB, with metastases greater than 5 cm in size in the retroperitoneal nodes. One patient was Stage III, with supradiaphragmatic metastases confined to the mediastinum and supraclavicular area. One patient was Stage IV, with evidence of extralymphatic metastases. The crude survival rate (corrected for intercurrent death, except for treatment toxicity) for the entire group was 87%. For Stage I, it was 91%, Stage IIA-80%, Stage IIB-75%, Stage III-100%, and Stage IV-0%. All patients had a minimum follow-up of 2 years with a range of 2 to 21 years. Evaluation of the Stage I patients reveals that 2500 rad in 3 weeks appears to be adequate in controlling microscopic disease, as there were no in-field recurrences when this dose was given. Those patients with Stage IIA and IIB disease who received greater than or equal to 3500 rad to macroscopic disease had 100% (7/7) survival and local control, while those receiving less than or equal to 3000 rad had a 66.6% (8/12) survival with three of four demonstrating persistent or recurrent abdominal disease. Thus, we feel that macroscopic disease requires 3500 rad to 4000 rad for control. All Stage II and III patients had planned mediastinal irradiation. No patients who received mediastinal irradiation recurred in the mediastinum. Whether this is because of our treatments or the natural disease process remains unanswered. Overall, we were able to salvage 12.5% (1/8) of our recurrences, while 37.5% (3/8) died from toxicity of their salvage therapy.(ABSTRACT TRUNCATED AT 400 WORDS)