• Anaerobic bacteria are prevalent in conjunctival flora but have not been adequately investigated as possible causes of endophthalmitis. The mean oxidationreduction potential (Eh) of the rabbit vitreous was found to be +25.1 mV, well within the limiting Eh value of many anaerobes. There was an oxygen pressure gradient in the vitreous ranging from 2.1 mm Hg immediately posterior to the lens to approximately 20 mm Hg adjacent to the medullary ray. Endophthalmitis was produced with pure cultures of Fusobacterium necrophorum, Propionibacterium acnes, and Peptostreptococcus magnus. Relatively small inoculates of F necrophorum caused severe, acute endophthalmitis with scleral perforation; P acnes and P magnus produced a self-limited endophthalmitis; and vitreoretinal fibrosis was a sequela of the Propionibacterium acnes infection.