OX2 (CD200) is a type-1 membrane glycoprotein that contains two immunoglobulin superfamily domains and which is expressed on a variety of lymphoid and non-lymphoid cells in the rat. The recent characterization of a receptor for OX2 (OX2R) on myeloid cells, and the phenotype of an OX2-deficient mouse, suggests that OX2 may regulate myeloid cell activity in anatomically diverse locations. Here we report the tissue distribution of the human homologue of the rat OX2 glycoprotein using a new monoclonal antibody (mAb), OX104, raised against recombinant human OX2. Human OX2 was expressed at the cell surface of thymocytes, B cells, T cells, neurons, kidney glomeruli, tonsil follicles, the syncytiotrophoblast and endothelial cells. This broad, but not ubiquitous, distribution pattern is very similar to that observed in rats, suggesting that OX2 may regulate myeloid cell activity in a variety of tissues in humans.