A patient with acquired immune deficiency syndrome with bilateral cytomegalovirus retinitis was treated with intravitreal 200-ug/0.1-ml doses of ganciclovir (9-[2-hydroxy-1-(hydroxymethyl) ethoxymethyl]guanine). The ganciclovir serum and intravitreal concentrations were measured with an enzyme-linked immunosorbent assay and pharmacokinetic factors were determined. There was no evidence of systemic absorption of ganciclovir from the eye. The elimination half-life of ganciclovir from the vitreous was estimated to be 13.3 hours. The intravitreal concentration remained above the ID50 of cytomegalovirus for approximately 62 hours after a single injection. Clinically, the patient retained useful vision in his right eye for three months. A total of 28 intravitreal injections were given on an outpatient basis under topical anesthesia and were well tolerated. There was no evidence of retinal toxicity from the drug.