The distribution of H-2 (Class I) and Ia (Class II) antigens in the mouse eye was determined with the use of monoclonal antibodies and found to be different. H-2 antigen was observed in the corneal epithelium, conjunctival epithelium, choroid, and inner and outer nuclear layer of the retina--in order of decreased intensity of staining. In contrast, Ia was detected most strongly, in a patchy distribution, in the choroid, limbus epithelium, and peripheral corneal stroma, followed by the iris and ciliary body. Thus, distinctively different patterns of distribution of H-2 and Ia were observed in the normal mouse eye. Surprisingly, adult eyes stained more intensely for both H-2 and Ia antigens than neonatal eyes, implying that the expression of MHC antigens varies with ontogeny. Since unique and important immunologic functions have been ascribed to class I and II antigens, their different distribution within the eye may indicate that various ocular structures can play distinctive roles in the immune response.