Using monoclonal antibodies 0.5 beta or G3-42, directed against V3 and C4 domains of glycoprotein 120 (gp120), we monitored the synthesis of oligomeric and monomeric forms of HIV-1 envelope glycoprotein 120 by flow cytometry or immunoprecipitation analysis in chronically infected MoIT-4 cells, cultured in the presence of tunicamycin. We observed that the inhibition of glycosylation by high concentrations of tunicamycin results in the reduction of an oligomeric gp120 on the surface of infected MoIT 4 cells as well as the decrease in the concentration of a monomeric form in the cytoplasm. Our studies revealed that the antibody 0.5 beta (exhibited higher sensitivity in the detection of gp120 than the antibody G3-42). We also observed that both antibodies did not recognise nonglycosylated precursor core envelope protein.