In group A, 36 HIV seropositive patients with CMV viruria receive a single dose of intravenous ganciclovir followed by one of three oral dose regimens for 28 days. Twelve individuals are treated at each dose level. In group B, 12 patients with AIDS and CMV retinitis receive oral ganciclovir therapy. These 12 patients must have received an induction course of intravenous ganciclovir for 4 weeks prior to study entry and must have stable CMV retinitis. Measurements for both groups include pharmacokinetics, safety, and tolerance (history, physical examination, hematology, and serum chemistry), and CMV blood and urine cultures. In addition, there are weekly ophthalmologic evaluations for individuals in the group B study.