We studied two patients, one with histologically confirmed endogenous bacterial retinitis associated with the acquired immunodeficiency syndrome and a second with ophthalmoscopically identical findings who also responded to antibiotic treatment. Both patients had focal, discrete patches of retinitis that enlarged slowly over weeks and ultimately accumulated large amounts of subretinal fluid and retinal exudate. One patient underwent retinal biopsy after systemic and vitreous cultures were negative. Histopathologic sections showed necrotic retina infiltrated with multiple histiocytes containing intracytoplasmic, iodine-positive, pleomorphic, encapsulated bacterial forms. The organism was not grown from the retinal biopsy specimen. Treatment with antibiotics resulted in improved vision in both patients. Our results indicate that endogenous bacterial infection should be considered in the differential diagnosis of retinitis associated with the acquired immunodeficiency syndrome.