The intermediate filament of mature human Sertoli cells is vimentin. A co-expression of vimentin together with cytokeratin has been demonstrated in Sertoli cells during embryonal development and under pathologic conditions in adult testes. We analysed the presence of vimentin, cytokeratin, and desmin in Sertoli cells of fetal testes (n=20), in seminiferous tubules of cryptorchid testes (n=10) and adjacent to testicular germ cell tumours (n=47) using specific monoclonal antibodies and single and double-labelling immunohistochemistry. During embryonal development prominent cytokeratin expression disappears after the 20th week of gestation. Interestingly, we also found desmin in immature intratubular Sertoli cells between weeks 11 and 14. In adult cryptorchid testes and in peritumour tubules, desmin was also prominently present in Sertoli cells in the vast majority of the cases investigated, as well as vimentin and cytokeratin co-expression. This first description of desmin immunoreactivity may shed some light on the ontogeny of human Sertoli cells and demonstrates that this cell type is able to express three types of intermediate filaments in a complex manner.