Cidofovir is arousing considerable interest as a new treatment for cytomegalovirus (CMV) retinitis. The agent is unique compared with currently available therapies, as it does not require viral enzymes for activation. Accordingly, it may overcome the resistance problems encountered by the nucleoside analogues, aciclovir and ganciclovir, which arise from acquired deficiency or alteration of the enzyme thymidine kinase. Cidofovir is now in phase III trials. An account of its safety and efficacy was presented at the 4th Triennial Symposium ‘New Directions in Antiviral Chemotherapy’ [San Francisco, US; November 1994].