30 patients with testicular cancer (20 seminoma, 10 non-seminomatous tumours) were investigated with respect to the determination of alpha-fetoprotein and beta-human chorionic gonadotropin in formalin-fixed slices by means of the indirect immunoperoxidase technique. The immunohistochemical method detected HCG-producing cells in 8 seminoma, whereas routine histology revealed syncytiotrophoblastic giant cells in 4 cases only. The immunohistochemical results and the serum AFT, and/or HCG values obtained by radioimmunoassay corresponded well in all patients with non-seminomatous tumours. Direct evidence of HCG production in the primary tumour can be important in therapeutic decisions, especially in patients with seminoma. The direct proof of AFP in the primary tumour might answer in the future the question of the incidence and the prognostic impact of yolk sac tumour parts in malignant teratomas.