Purpose To determine the effect of exogenous interleukin-1alpha; (IL-1alpha;) on the retina and its vasculature and VEGF expression in SD rats． Methods IL-1alpha;2．0 ng (20 mu;l) were injected into the vitreous of 8 left eyes of 8 SD rats while steriled PBS were injected into 8 right contralateral eyes of the same rats as control． All eyes were assessed by direct ophthalmoscopy every day and enucleated on the 7 thpostoperative day． Histological examination (hemato xylineosin staining) and immunohistochemical staining with antibody against VEGF antigen were performed， and sections were observed and photographed under light microscopy． Results ①All 8 IL-1alpha; inject ed eyes developed epiretinal membranes and extraretinal neovascularization on the 3 rd postoperative days while none of the 8 control eyes exhibited any a bnormal retinal vascular changes and they were confirmed by HE staining;②Immuno staining identified VEGF express mainly in the inner layer of vessel walls， the epiretinal membranes， the neuroganglional layer and the photoreceptor layer of retina， while the control eyes showed only weak positive staining in the photo receptor layer． Conclusions IL-1alpha; is capable of inducing vitreo retinal neovascularization，and increasing the expression of VEGF in the retina and epiretinal membranes． (Chin J Ocul Fundus Dis, 2001,17:135-137)