Mild argon laser burns produced in the retina of cynomolgus monkeys underwent differentiated retinal repair with frequent restoration of the pigment epithelial barrier. Permeability of the restored barrier was tested by two tracers injected intravenously--horseradish peroxidase followed by electron microscopic evaluation and fluorescein sodium followed by fluorescence microscopic examination of freeze-dried tissue. Tightness of the barrier was associated with regularly arranged pigment epithelial cells joined by zonulae occludentes. Leakage of the barrier was associated with discontinuities in the line of regularly proliferated pigment epithelial cells. At times, the tracers stained the pigment epithelial cells diffusely but they did not accumulate in the subretinal space. Variable changes in the choriocapillaris were noted. Mild photocoagulation may be effective in treating central serous choroidopathy in man when restoration of the pigment epithelial barrier is stimulated.