The vascularization of 50 tumors of the central nervous system (CNS) including 17 meningiomas, 25 neuroectodermal tumors, i.e., astrocytomas, oligodendrogliomas, mixed gliomas, glioblastomas, medulloblastomas, seven metastatic carcinomas, and one malignant hemangioendothelioma were investigated using biotinylated Ulex europaeus type I lectin (UEA I) in an indirect avidinbiotin-peroxidase procedure. The cytochemical staining pattern of UEA I on paraffin sections was compared with that of biotinylated Dolichos biflorus lectin (DBA), and with the immunocytochemical staining of factor VIII related antigen (F VIII/RAG) by polyclonal antisera using the PAP technique. UEA I visualized the endothelia of blood vessels with equal intensity, sensitivity, and reliability in normal brain and in tumor tissue with neovascularization. While large, medium, and small vessels were equally well demonstrated by UEA I and antibodies against FVIII/RAG, capillaries and endothelial sprouts were stained more consistently and intensely by UEA I. No reliable cytochemical staining could be obtained by DBA regardless of tissue or cell type investigated. It is concluded that UEA I is a highly useful cytochemical marker for the identification of vascular endothelia in paraffin sections of human brain tumors.