The serum levels of human chorionic gonadotropin (HCG), alphafetoprotein (AFP), lactic dehydrogenase (LDH), and carcinoembryonic antigen (CEA) were measured in 62 men with advanced nonseminomatous germ-cell testicular tumors. The HCG level was elevated in 64%, the AFP level in 67%, and the LDH level in 62%, including three of the six men with normal levels of the other two markers. At least one of these three markers was elevated in 91% of patients. Sustained or rising levels of HCG or AFP always were accompanied by persistent or recurrent tumor. Carcinoembryonic antigen was found not to be a useful marker in testicular cancer. Patients whose tumors contained yolk-sac elements always had elevated AFP levels, and patients with choriocarcinoma always had elevated levels of HCG. However, absence of these histologic types did not preclude elevations of the respective markers. Tumor markers are indispensable in the management of patients with testicular cancer, and several markers must be measured repeatedly if the greatest percentage of patients is to benefit.