The cellular toxicity and anti-human immunodeficiency virus (HIV)-1 activity of stepronin was evaluated.Zidovudine (AZT) and suitable drug-free controls were used in assays with peripheral blood mononuclear cells (PBMC) and monocyte-derived continuous cell lines U937 and CEM-4.Stepronin affected the lice cycle of HIV-1 in infected cultured cells.An antiviral activity was measured by inhibition of viral p24 antigen productionAt a concentration of 10 μmol/L, an increment of viral p24 antigen was observedThe inhibition of HIV-1 by this drug was not dose-dependent in a linear fashion, as inhibition is for HIV-1 by AZT.