Povidone-iodine is frequently instilled on to the conjunctival surface prior to intraocular surgery in order to prevent septic endophthalmitis. A small amount of povidone-iodine is inevitably introduced into the eye when it is used in this manner. The toxicity of intravitreal povidone-iodine was assessed in rabbit eyes by injecting 0.1 ml of povidone-iodine in concentrations of 0.05%, 0.5% and 5% into the vitreous cavity. The injected eyes were evaluated by clinical examination, anterior segment and fundus photography, endothelial cell counts, electroretinography and histopathology. Compared to control eyes, no changes were observed in all 6 eyes injected with 0.1 ml of 0.05% povidone-iodine solutions. 9 of 10 eyes tolerated a concentration of 0.5% with no detectable adverse changes. One eye developed a temporary mild iritis and mild suppression of the ERG. Intraretinal hemorrhages, edema, arteriolar narrowing and retinal edema were seen one week following injection. Mild retinal necrosis of the same area was seen on histology. All 4 eyes injected with 5% povidone-iodine developed temporary hypotony and iridocyclitis. A dense cataract developed in all eyes. Full thickness retinal necrosis and a profound lasting reduction in the ERG was produced in all of these eyes. No corneal epithelial or endothelial changes were observed in any eye in this series. Low concentrations of intravitreal povidone-iodine likely to be produced by instillation prior to surgery are tolerated by rabbit eyes. The concentrations tolerated by the studied eyes are near reported bactericidal levels.