V3 loop peptides from three different human immunodeficiency virus type 1(HIV-1)strains were synthesized.BH10,ADA,and 89.6 strains whose infections are dependent on CXCR4,CCR5,and both,respectively, were selected.Co-transfection of luciferase reporter gene and corresponding envelope genes (HXB2, ADA, and 89.6) generate pseudotype viruses (HXB2/Luc, ADA/Luc, and 89.6/Luc). The effects of each peptide on the infection of U87 cells expressing CD4 and one of the coreceptors with all pseudotype viruses were evaluated. V3 loop peptide from BH10(V3-BH10)alone increased the HXB2/Luc infection by 93% at 10lM. Both V3-ADA and V3-89.6 enhanced ADA/Luc infection by 38% and by 55% at 10lM,respectively.For 89.6/Luc infection,only V3-89.6 enhanced the infections on both target cells.V3-BH10 modulated the epitopes of coreceptor binding site and V2 loop of gp120 on HIV-1 ⅢB infected H9 cells, indicating that V3 loop peptide activates viral gp120 and enhances infectivity.