Five immunocompromised patients, four with AIDS and one who had undergone bone marrow transplantation, showing ocular signs of cytomegalovirus retinitis, were treated with 9-(2-hydroxy-1-(hydroxymethyl)ethoxymethyl) guanine (Ganciclovir), given intravenously at the dose of 5 mg/kg twice daily for a period ranging from 10 to 20 days. At the end of the treatment, in 4 of 5 patients, the ophthalmoscopic picture had improved, with reduced exudation and an arrest in the progression of retinal necrosis, the pattern clearly indicating a trend towards organization and scarring. Complete resolution of the retinitis without subsequent relapse was observed only in the bone marrow transplant patient, who recovered immunologically, whereas improvement of the eye involvement was only transient in the three AIDS patients.