Novel aryl phosphate derivatives of the anti-HIV nucleoside analogue AZT have been prepared by phosphorochloridate chemistry. These materials were designed to act as membrane-soluble prodrugs of the bioactive free nucleotides. In vitro evaluation revealed the compounds to have a pronounced, selective anti-HIV activity in CEM cells; the magnitude of the biological effect varied considerably depending on the nature of the phosphate blocking group. Moreover, several of the compounds retain marked antiviral activity in TK- (thymidine kinase-deficient) mutant CEM cells in which AZT was virtually inactive. These data strongly support the hypothesis that the AZT phosphate derivatives exert their biological effects via intracellular release of AZT nucleotide forms and suggest that the potential of nucleoside drugs in antiviral chemotherapy may be enhanced by suitable nucleotide delivery strategies.