Normal testicular tissue and primary and metastatic testicular germ cell tumours were examined for their intermediate filament protein (IFP) expression. Seminomas were shown to react with antibodies to vimentin, while non‐seminomatous germ cell tumours were strongly positive with antibodies to cytokeratin. In the case of teratocarcinoma, several components of the tumour can be distinguished using a combination of monoclonal and polyclonal antisera in the double‐label immunofluorescence technique. We conclude that antibodies to cytokeratin and vimentin can be helpful in the diagnosis of testicular germ cell tumours, especially in the differentiation between seminomas and non‐seminomatous testis tu