Thirty-seven carcinomas with histologically verified lymphatic vascular invasion were evaluated with five endothelial cell markers in order to test these markers for the objective documentation of the vascular invasion. The markers were factor VIII-related antigen (FVIII), BNH9 monoclonal antibody to H antigen,Ulex europaeusI lectin (UEA),Psophocarpus tetragonolobuslectin (PT), and CD34, a leukocyte antigen also present in endothelial cells. All of these markers stained small and medium-sized normal vessels approximately equally in formalin-fixed, routinely processed tissue. However, all except for FVIII had additional specificities. BNH9 also stained all erythrocytes. BNH9, UEA, and PT reacted with epidermis and some carcinomas. CD34 also stained peritumoral fibroblasts both around tumor nests and vessels, obscuring the labeling of vascular invasion spaces; therefore, this marker was not further evaluated. The four markers could detect the presence of invasive tumor cells in the confines of an immunohistochemically or lectin histochemically detectable vessel as follows: FVIII, 23/37 cases; BNH9, 28 cases; UEA, 30 cases; and PT, 21 cases. Obvious intravascular (lymphatic) spaces with deposits of tumor cells were commonly negative for vascular endothelial cell markers. This may result from antigenic or anatomic destruction of vascular endothelium, or from problems of specimen-to-specimen optimization of immunohistochemistry. Although the identification of endothelial cells directly underneath the invasive cells supports the presence of vascular invasion, such invasion cannot be ruled out by negative immunostainings for endothelial cell markers.