Three congenic Royal College of Surgeons (RCS) strains of rats have been developed: the RCS-p+ strain, which is a black-eyed dystrophic strain; the pink-eyed RCS-rdy+ strain, which is wild-type (+/+) at the retinal dystrophy (rdy) genetic locus and serves as the control for the inbred, pink-eyed RCS strain; and the black-eyed RCS-rdy+p+ strain, which is +/+ at the rdy locus and serves as the control for the black-eyed RCS-p+ line. Several cytologic features of the photoreceptors were examined in the two control strains, including percentage of cone cells, rod outer segment lengths in different hemispheres of the eye and in different lighting conditions, rate of rod outer segment renewal, and the cyclic pattern of rod outer segment disc shedding. In the pink-eyed RCS-rdy+ strain these features were the same as those in previously described albino rat strains. Most of these features have not been described previously in fully pigmented rats. In the black-eyed RCS-rdy+p+ strain, rod outer segments in the superior eye hemisphere were about 50% longer than those in the inferior hemisphere. The rate of rod outer segment disc synthesis was the same in both hemispheres. Consequently, rod outer segment renewal time depended on outer segment length. This ranged from 9 to 10 days in the inferior hemisphere to 14.6 days in the superior hemisphere.