A condition similar to massive periretinal proliferation in man can be produced in rabbits by injecting homologous fibroblasts into the vitreous. We have studied the effect of daunomycin, a cytotoxic drug, in this model to determine a dose which would not be toxic to the retina but would be effective in preventing proliferation of the injected fibroblasts and eventual retinal detachment. The results of this study demonstrate that daunomycin at a dose of 9 nmol per eye reduces the incidence of retinal detachment by over 50%. Doses higher than 30 nmol per eye are toxic to the retina.