Changes in the cell membrane glycolipid composition and metabolism are frequently associated with carcinogenesis. The accumulation of globo-series glycolipids is the most notable change of the germ cell glycolipid composition observed in testicular tumours. In this study, the expression of the globo-series core-structure, globotriaosylceramide (Gb3) was investigated in the preinvasive stage of testicular germ cell tumours, carcinoma in situ (CIS). Seventeen tissue specimens with CIS and 12 samples of overt testicular tumours were immunostained with anti-Gb3 monoclonal antibody 38-13. The accumulation of Gb3 was detected in 12 CIS samples (70.6%) and in 8 invasive tumour samples (66.7%), including seminoma, non-seminoma and a combined germ cell tumour. Our findings indicate that the composition of glycolipids shift at the common preinvasive stage of testicular germ cell tumours and confirm that Gb3 is a tumour-associated antigen of testicular germ cell neoplasia.