Current treatment of cytomegalovirus retinitis in patients with acquired immunodeficiency syndrome involves frequent intravenous administration of sodium ganciclovir that often results in unacceptable side effects. We have developed devices that release ganciclovir at rates of 2 micrograms/h and 5 micrograms/h in vitro. When implanted into the vitreous of rabbit eyes, mean intravitreal ganciclovir levels of 9 mg/L and 16 mg/L were maintained for more than 80 and 42 days, respectively. Devices were well tolerated, with no toxic effects attributable to the polymers used in the devices. This investigation indicates that these devices can maintain therapeutic levels of drug for extended periods and are well tolerated in the rabbit eye. They may prove useful in the clinical management of cytomegalovirus retinitis in patients with acquired immunodeficiency syndrome.