We examined the localization of protein kinase C (PKC) in the rat retina, using a monoclonal antibody against PKC. The PKC immunoreactivities were localized in bipolar cells as reported previously, and also in outer and inner segments (OS and IS) of photoreceptor cells. As the PKC immunoreactive OS and IS of photoreceptors were very few in number, we hypothesized that these were of cone photoreceptors. We then examined whether the PKC immunoreactive OS and IS were bound by peanut agglutinin which was shown to bind specifically to cone OS and IS. Almost all of the PKC immunoreactive OS and IS showed PNA binding.