Testicular tumor tissues and various normal tissues were examined by immunohistochemical techniques for expression of globotriaosylceramide (Gb3) using anti-Gb3 monoclonal antibody (1A4). In formalin fixed paraffin-embedded specimens (31 cases), Gb3 was positive for every kind of elements of testicular germ cell tumors, especially it's incidence of positive staining were 100% in seminomas (16/16) and embryonal carcinomas (6/6). On the other hand, four cases of testicular malignant lymphoma were all negative for Gb3, and some normal testicle, liver, kidney, pancreas, spleen, ileum and rectum showed very weak reactivity with 1A4. In frozen materials (10 cases), similar incidence of positive staining with that of paraffin-embedded specimens were observed in drying only manner, 4% parafolm-aldehyde fixation following drying and 10 min. of acetone fixation following drying. Incidence of very strong staining in testicular germ cell tumors were as follows, 7/10 in 4% parafolmaldehyde fixation, 6/10 in drying only, 4/10 in 10 min. of acetone fixation and 7/22 in paraffinembedded specimens. Fixation with 30 min. of acetone fixation and 10 min. of 90% ethanol and treatment with 10 min. of chloroform:methanol (2:1, v/v) extremely decreased the reactivity with 1A4, suggesting that Gb3 exists mainly as glycolipid. Gb3 may thus be a useful histological marker for testicular germ cell tumor, and the tissue should be treated with the process of freezing followed by 4% parafolm-aldehyde fixation, drying only or 10 min. of acetone fixation, and formalin fixed paraffin-embedded specimens were also available enough.