Six patients (11 eyes) with virologically confirmed cytomegalovirus (CMV) retinitis involving the posterior pole of the eye were treated with a new drug, ganciclovir. Treatment with intravenous ganciclovir consistently halted progression of retinitis and produced improvement in measures of visual function. However, within three weeks after cessation of therapy renewed CMV activity and worsening of visual function were observed in most cases. Maintenance therapy with ganciclovir extended the period of remission from CMV retinitis.