Cytomegalovirus (CMV) encephalitis has been reported with increasing frequency in patients with AIDS. Nevertheless, the management of CMV-related encephalitis appears to be problematic and data in the literature on the clinical efficacy of ganciclovir therapy is sparse and controversial. We describe two patients with AIDS who developed CMV encephalitis while receiving ganciclovir maintenance therapy for CMV retinitis. Moreover, there was no improvement in neurological status or virological and radiological response during a further induction course of ganciclovir. These observations suggest that the currently recommended therapeutic protocols with ganciclovir are not effective in the prevention and treatment of CMV encephalitis in patients with AIDS.