CMV retinitis is a severe vision-threatening viral infection of the retina of the eye. It occurs in patients whose immune function has been impaired and is the most common cause of blindness in patients with AIDS. Ganciclovir (GCV) improved the signs and symptoms of CMV retinitis in approximately 80 percent of the patients treated for 2 weeks, but almost all of the patients treated with GCV had a relapse after treatment was stopped. Thus, it is important to determine if GCV can be safely given over a long period of time (maintenance therapy) and if it is effective in preventing a relapse of CMV retinitis.