Two distinct gap junction proteins (connexins) are expressed in rat corneal epithelium in a way which parallels cellular differentiation processes in this tissue. Connexin43 is restricted predominantly to the basal cells of the corneal epithelium and is present in significantly reduced amounts compared to the situation in the adjacent conjunctival epithelium. In contrast, a gap junction protein recognized by antibodies against MP70 which is the ovine homolog of mouse connexin50, is strongly expressed in the corneal epithelium and is present in the basal cells, wing cells and surface cells. While the functional significance of this differential expression of corneal epithelial connexins has yet to be established, the corneal epithelium is the third avascular tissue besides lens and heart valves which expresses a gap junction protein recognized by anti-MP70 antibodies.