Panretinal photocoagulatlon was carried out in mini pigs in an attempt to elucidate the mechanisms involved in laser therapy. The effect of the vitreous from these eyes on the proliferation of retinal microvascular endothelial cells was then studied. Vitreous removed 4 days after panretinal photocoagulation had no effect on the proliferation of bovine retinal microvascular endothelial cells in basal medium but inhibited proliferation in growth medium. Control vitreous was mitogenic for the microvascular cells in basal medium but this effect was not observed in growth medium.