61 patients with seminoma and 113 with nonseminomatous germ cell tumors of the testis were treated according to the histology, stage of disease, and serum levels of tumor markers (CEA, AFP, hCG, hPL and SP1). 33 were stage I, 63 stage II, and 78 stage III patients. Most patients with seminoma, mature teratoma, immature teratoma, and ‘pure type’ embryonal carcinoma, as well as the latter three types with seminomatous admixture, had normal serum levels of the markers. Sometimes, slightly elevated levels of hCG suggested the presence of metastases. But, serial measurements of the markers were seldom useful in monitoring therapy. The 5-year tumor-free survival rates were favorable: 100% for stage I and II disease; and 57 or 44% for, respectively, stage III seminoma or the other tumors amounting to 10% of the nonseminomatous group. The role of the five markers was significant in patients with teratoma with malignant transformation, choriocarcinoma, endodermal sinus tumor (EST), and embryonal carcinoma or teratocarcinoma with an admixture of EST or choriocarcinoma or both. Elevation of a marker was a grave prognostic sign. The 5-year survival rates were 100, 16, and 4% for stages I, II and III disease, respectively. An elevated level of one or more of the markers assayed was always useful for monitoring therapy. Decreasing level indicated regression. However, return of an elevated level to normal did not indicate eradication of all tumor and called for diagnosis by imaging modalities. Constantly elevated or increasing marker levels during treatment indicated resistance to therapy. An increasing level from any nadir during remission indicated recurrence. Elevated levels of any of the five markers tested were as important as imaging modalities, and often more sensit