CMV retinitis occurs in 20 to 30 percent of patients with AIDS and is the leading cause of visual loss in these patients. At present, ganciclovir and foscarnet are the only drugs that have been approved by the U.S. Food and Drug Administration for the treatment of CMV retinitis. The therapeutic regimen for each drug consists of a 2-week induction period followed by daily maintenance intravenous infusions. Unfortunately, CMV retinitis usually progresses despite daily maintenance therapy, and both drugs are associated with significant systemic toxicity that often limits their therapeutic usefulness. As an alternative to intravenous administration, direct intravitreal injections of ganciclovir have been studied and have been shown to be effective in delaying the progression of CMV retinitis. The short half-life of the drug, however, necessitates one to two intraocular injections a week to maintain therapeutic levels. Widespread adoption of this technique has been limited because of the logistical difficulties and inherent risks associated with numerous intravitreal injections.