The retinal pigment epithelium of normal adult golden Syrian hamsters was examined by light and electron microscopy, using conventional and enzyme histochemical techniques. Hamster retinal pigment epithelium was composed of a single layer of cuboidal cells that had marked infolding of the basal cell wall and numerous microvillous processes extending from the apical surface. Melanin content varied within each specimen and there appeared to be incomplete or aberrant development of many melanin granules. Many incompletely melanized granules showed acid phosphatase activity. There were the usual cell organelles, including mitochondria, smooth and rough-surfaced endoplasmic reticulum, ribosomes, and Golgi complexes. Large phagosomes increased in number in the morning hours. Autophagic vacuoles and small lipid droplets were commonly seen. Occasional basal bodies, cilia, and root filaments were found. In two specimens, a curious intranuclear para-crystalline structure was observed.