A 55-year-old man with the acquired immunodeficiency syndrome had cytomegalovirus (CMV) retinitis develop in his left eye. The patient declined treatment with ganciclovir but elected to be treated with zidovudine. Two months later his CMV retinitis regressed, and it remained inactive for a total of 9 months. The most likely explanation was zidovudine-mediated improvement in the patient's immune function with subsequent suppression of the CMV retinitis in the left eye. The patient ultimately and preterminally had CMV retinitis develop in his right eye. He subsequently died and his eyes were examined at autopsy. Active CMV retinitis lesions were noted in the right eye while inactive scars were noted in the left eye. Immunoperoxidase staining and in situ hybridization studies demonstrated the presence of CMV in the right eye but not in the left eye. While ganciclovir remains the treatment of choice for CMV retinitis, zidovudine treatment may have a beneficial effect on CMV retinitis in some patients.