Diaryl phosphate derivatives of the anti-HIV nucleoside analogue AZT were prepared as potential pro-drugs of the bio-active free nucleotide. The compounds are potent inhibitors of HIV replication in several cell lines, and show reduced cytotoxicity in vitro, by comparison to the parent nucleoside. However, in contrast to previously reported aryloxy phosphoramidate derivatives of AZT the diaryl phosphates are poorly active in HIV-infected thymidine kinase-deficient CEM cells.