The highest prevalence of testicular cancer occurs in young men with high androgen activity. The presence and distribution of androgen receptors (ARs) was therefore investigated in germ cell neoplasia, using two specific monoclonal antibodies. Tissue samples from 18 patients with seminoma and/or carcinoma-in-situ (CIS) of the testis were examined. An indirect immunohistochemical method with a biotin-streptavidin-peroxidase or an alkaline phosphatase detection system was used. 45% of seminoma samples and 42% of CIS samples were AR-positive with antibody AN 1-15. The values obtained using antibody F 39.4.1 were 44 and 40% respectively. Some differences in specificity between the two antibodies were observed. Unusual granular staining of germ cells in normal testes, also present in malignant germ cells, was noted when antibody F39.4.1 was used. The presence of AR protein immunoreactivity in neoplastic germ cells suggests that androgens may be involved in the pathogenesis of the disease.