Occupational analyses were conducted between 1971 and 1978 comparing 165 cases of testicular cancer in the Hannover region of Germany with 187 controls without neoplastic diseases admitted to the Hannover University Medical School during the same period. The results showed a significantly higher risk of metal workers developing seminomas and mixed seminomatous tumors compared to the controls (odds ratio 2.05; 1.17-3.58). There was a lack of risk for the nonseminomatous tumors as a whole group, and cases with a history of metal work may have a decreased risk for embryonal carcinomas. No definite single noxious substance responsible for the development of testicular tumors could be detected. In view of the results in animal experiments, cadmium and zinc are especially considered in the discussion.