Injection of a 15-micron microsphere suspension through one or two vortex veins of nine monkey eyes caused various degrees of sectorial choroidal ischemia, which were documented by fluorescein angiography and electron microscopy. The severity of the lesions to the fundus depended on the volume of microspheres injected (0.4 to 1.6 ml of a suspension of 600,000 microspheres/ml). Three hours after embolization white patches appeared in the retinal pigment epithelium as well as a posterior pole serous retinal detachment in five eyes. Delayed choroidal filling was noted in the quadrant involved, but a few choriocapillaris units slowly perfused, leading to fluorescein leakage in the serous retinal detachments. Histologic examination showed various types of damage to the retinal pigment epithelium, including vacuolization and cell membrane rupture.