Lens-induced granulomatous endophthalmitis is an experimental autoimmune disease produced after lens injury in rats previously sensitized to lens protein. The disease is histopathologically virtually identical to the human disease known as phacoanaphylactic endophthalmitis. A number of observations have suggested that an immune-complex mechanism is important in the pathogenesis of this disease. The C3 inactivator from cobra venom is known to inhibit inflammation in a variety of immune-complex-mediated diseases. We observed that in animals treated with this inactivator, the development of experimental lens-induced granulomatous endophthalmitis is markedly suppressed. The results of this study lend support for the role of an immune-complex mechanism in the pathogenesis of lens-induced endophthalmitis.