Retinal embolism was produced in the owl monkey with autologous fibrin clot and the resultant damage studied by high speed fluorescein cinematography. Pictures were taken at 64 frames per second with 16-mm film and 24 frames per second with 35-mm film. The pattern of retrograde collateral flow was followed as it occurred. Often, emboli were present in the retinal arteries which were not observed until contrast studies were performed. Fibrin clot appeared to cause endothelial damage during passage, which was manifested by fluorescein leakage from arteries.