AbstractA case of a 68-year old man with intestinal bleeding caused by a small hemangiosarcoma in the jejunum is reported. Tissue specimens were examined by light microscopy with classical histochemical techniques and the immunogold-silver staining method in combination with silver acetate autometallography. Monoclonal and polyclonal antibodies to various tissue type markers and lymphocyte associated antigens were employed. Factor VIII-related antigen was negative in the neoplastic cells but positive in most endothelial cells of veins and some capillaries of the adherent tissue. However, antibodies to vimentin, the endothelial marker BMA 120, and Ulex europeus I agglutinin (UEA I) lectins gave strongly positive reactions throughout the lesion and in endothelial cells of all vessels. T lymphocytes as well as neuronal and glial structures were detected between the proliferating cells. (The J Histotechnol13:141, 1990)