The antiviral activity of 3'-azido-2',3'-dideoxynucleoside 5'-phosphate analogues: 5'-phosphonomethylene-3'-azido-2',3'-dideoxythymidine, 5'-methylphosphonate and 5'-phosphite of 3'-azido-2',3'-dideoxythymidine, 5'-phosphites of 3'-azido-2',3'-dideoxyadenosine and guanosine was investigated in HIV-infected cell cultures (human lymphoblastoid cells). The effectivity of inhibition of HIV-reproduction in cells by these substances was close or even higher than that for the corresponding 3'-azido-2',3'-dideoxynucleosides, whereas their toxicity was lower than that of nucleosides. These substances are supposed to be transported into the cells and to be transformed into the corresponding 5'-triphosphate analogues under the action of cell kinases. It is possible that such agents are terminator substrates of virus reverse transcriptases and thus inhibit the biosynthesis of DNA chains.