In this study we examined 198 sarcomas, 38 carcinomas, 13 'tumours with a spindle cell component' and 22 malignant melanomas with a commercial monoclonal vimentin antibody. All histopathological material was formalin fixed and paraffin embedded. The results show this antibody to be a sensitive and specific marker of mesenchymal derivation or differentiation. It is a useful tool in separating sarcomas from most carcinomas, and in separating malignant melanomas from carcinomas. When used in combination with a cytokeratin antibody it identifies carcinosarcomas and synovial sarcomas.