Recent reports by this laboratory and others have demonstrated an association between 5A11/Basigin, a member of the immunoglobulin gene superfamily, and monocarboxylate transporter-1 (MCT1), a lactose transporter. Indeed, it was determined in the 5A11/Basigin null mouse retina that MCT1 does not properly integrate into the cell membranes of Müller cells (MCs) or the retinal-pigmented epithelium, where the two are colocalized. The purpose of this study was to elucidate the association of 5A11/Basigin and MCT1 in the developing mouse retina. Immunocytochemical localization and real-time RT-PCR were used to evaluate the expression and localization of 5A11/Basigin and MCT1 at embryonic days 12, 15, and 18, as well as post-natal days 1, 7, 14, and 21. Expression of both proteins progressed from a more generalized distribution throughout the undifferentiated neural retina to specific staining of retina-pigmented epithilia, the MCs, photoreceptor cells and the ciliary apparatus. Although these two membrane glycoproteins were often colocalized, distinct differences in the location and magnitude of their expression over time was observed. These findings suggest that although 5A11/Basigin and MCT1 can associate within the cell membrane, their expression is not always associated and colocalized.