Rats that receive intravenous injections of sodium iodate develop a retinopathy characterized by the partial loss of the retinal pigment epithelium (RPE). In thin sections examined by transmission electron microscopy the choriocapillaris atrophied adjacent to areas of RPE destruction. The endothelial cells thickened and lost their fenestrae and the lumen of the capillary was reduced. At sites where the RPE remained normal in appearance the choriocapillaris did not atrophy. Scanning electron microscopy of vascular casts of the choriocapillaris showed the coexistence of atrophic and normal choriocapillaris throughout the retina, presumably adjacent to sites where the RPE was destroyed or spared, respectively. Our observations support the concept that the RPE exerts some control over the structure and function of the choriocapillaris.