We produced monoclonal antibody TS-SC6 specific for 33kDa protein (33K) from bovine retina and studied the localization of 33K in mammalian retinas (rat, mouse, bovine, guinea pig and human) and pineal gland of rat. An immunohistochemical study showed that TS-SC6 reacted with the outer plexiform layer (OPL), outer nuclear layer (ONL) and rod inner segments (IS) in rat, ONL, IS and IS in mouse and guinea pig. It reacted with ONL and rod outer segments (OS) in bovine, ONL and OS in human. Immunoreactivity was seen in the pineal gland, but there was no immunoreactivity in the central nervous system surrounding the pineal gland. Immunoblot analysis was carried out with soluble fractions prepared from the retina, pineal gland, cerebrum, liver, kidney and intestine of rats. TS-SC6 reacted with 33K of the retina and pineal gland, respectively. However, it did not react with soluble fractions from the other tissues.