The anti-HIV activity of niglizin (penta-O-nicotinate of glycyrrhizic acid) and of its combinations was studied in the culture of infected MT-4 cells and in respect to the recombinant reverse HIV-1 transcriptase. Niglizin was shown to suppress effectively the HIV replication and to be a noncompetitive inhibitor of reverse transcriptase. Research of a combined anti-HIV action of niglizin and of azidothimidine (AZT) demonstrated that the preparations, when used at ratios of 1:20, 1:50, 1:200 and 1:2000, suppressed the synergetic effect both in the cell culture and in the recombinant reverse HIV transcriptase. A study of the antiviral activity of niglizin and of its joint use with AZT in respect to the AZT-resistant HIV-1 mutant showed niglizin to be more effective (ID50 = 0.134 microM) versus the "wild" strain. (ID50 = 9.64 micriM); whereas, its combined use AZT:niglizin = 1:100 displayed synergism (FIC = 0.553). The efficiency of the combined AZT/niglizin anti-HIV effect both in respect to the "wild" strain and to the AZT-resistant mutant confirms that such combinations are promising for the treatment of HIV infection.