HLA DR and DQ distribution was investigated in normal human ocular tissues, together with class I antigens and immunocompetent cell subsets, by immunofluorescence and immunoperoxidase procedures. In the anterior segment, our findings, consistent with those of previous reports, showed the wide distribution of class I antigens, specially in the corneal epithelium, while class II antigens were restricted to very rare cells scattered in the conjunctiva, the peripheral cornea and the stroma of the ciliary processes. Some non pigmented epithelial cells of the ciliary processes were HLA DR and DQ positive. In the posterior segment, class I antigens were abundantly represented in the choroid and the retinal layers. Few HLA DR and DQ positive cells were seen in the choroid, similar to those found in the anterior segment. Normal RPE did not react with any monoclonal antibody, but numerous cells located in the retina were strongly HLA DR and DQ positive, all around the blood vessels, and not at the sites of endothelial cells. The characterization of those cells, which could be hypothetized as pericytes needs further studies but suggests close relationships between neuroretina and the immune system. This study may provide insight in the implication of the immune system in many poorly understood ocular diseases.