This study evaluated the immunohistochemical staining of four endothelial cell markers in well differentiated and poorly differentiated areas of angiosarcomas. Formaldehyde-fixed, paraffin-embedded sections from eight angiosarcomas were studied using the antibodies anti-factor VIII-related antigen (FVIII-RA), Ulex europaeus I agglutinin, anti-CD34 (QBEND/10) and anti-CD31 (JC70). The immunostaining of the angiomatous (well differentiated) and solid (poorly differentiated) areas was separately analysed and specificity was evaluated in 20 non-vascular tumours. The antibody anti-CD31 and Ulex europaeus were the most sensitive markers staining well differentiated vasoformative structures and poorly differentiated solid areas. Anti-FVIII-RA and anti-CD34 did not stain undifferentiated malignant endothelial cells from solid areas. Ulex europueus and anti-CD34 showed very low specificity; in contrast, none of the non-vascular tumours expressed CD31 or FVIII-RA. JC70 (anti-CD31) appears to be the most useful marker in elucidating the vascular nature of angiosarcomas. Is important to emphasize the lack of specificity of Ulex europaeus and the low sensitivity of anti-CD34 and anti-FVIII-RA for poorly differentiated lesions.