Phosphate derivatives of the anti-HIV nucleoside analogue AZT were prepared as potential pro-drugs of the bio-active free nucleotide. In marked contrast to the parent nucleoside AZT, several of the derivatives are active inhibitors of HIV in kinase-deficient cells. The precise activity varies greatly with the phosphate structure, data consistent with a mode of action involving intracellular hydrolysis to release the bio-active nucleotide forms.