Endothelial cell-specific molecules are potential targets for new therapeutic strategies in the control of inflammatory reactions, immune responses and neoangiogenesis. We describe the production and characterization of MEC 14.7, a monoclonal antibody directed to murine endothelial cells recognizing a glycosylated protein with an apparent molecular mass of about 100 kDa in cultured endothelioma cell lysate and about 80 kDa in lung lysate. MEC 14.7 antigen was selectively expressed by the endothelium in vivo, particularly in small vessels and neoformed capillaries and by developing vascular structures in embryonal bodies. Deglycosylation of the molecule with neuraminidase, O- and N-glycanase showed that the MEC 14.7 epitope is neuraminidase-sensitive. MEC 14.7 antigen was purified from lung lysates by chromatographic techniques, and sequenced internal peptides indicated it was identical with murine CD34. Thus the apparent molecular mass of CD34 is heterogeneous, depending on the glycosylation state in the different cell types. Immunomagnetic isolation and culture of MEC 14.7-positive bone marrow cells showed that this antibody recognizes hematopoietic progenitors (particularly myelomonocytic) and can be used in murine models of bone marrow reconstitution.