The cone-specific monoclonal antibody, CSA-1, selectively labels cone photoreceptors in the neural retina. Immunofluorescence assays reveal that CSA-1 binds cone outer and inner segments, cell bodies, axons and synaptic pedicles. The binding of the antibody is membrane-associated, not cytoplasmic. Several lines of evidence, including sensitivity to mild alkaline hydrolysis and galactosidic enzymes, suggest that the CSA-1 detected determinant is a galactose-containing carbohydrate moiety. Immunoblotting analyses show CSA-1 immunoreactivity with at least two molecules of 54,000 daltons that differ slightly in isoelectric point, and an additional, higher molecular weight species. CSA-1 should prove to be of value in studies of cone photoreceptor biology, in analyses of the development and differentiation of these cells, and in assessing their fate in various retinal pathologies.