The human immunodeficiency virus type 1 (HIV-1) gp41 plays an important role in membrane fusion between viruses and target cells. The gp41 ectodomain contains two heptad repeat regions adjacent to the N and C-termini. Peptides derived from these two regions, designated N and C-peptides, are potent inhibitors of HIV-1 infection and can interact with each other to form a six-stranded coiled-coil, representing the fusogenic core structure of gp41. A monoclonal antibody was generated, designated NC-1, which specifically binds to the complex formed by the N and C-peptides, but not to the individual peptides. An enzyme linked immunosorbent assay (ELISA) was developed using NC-1 for detecting complex formed by N and C-peptides and for screening of organic compounds for antiviral agents that may interfere with complex formation and inhibit HIV-1 infection. Single point mutations in the C-peptides abolish the complex formation also eliminate their anti-HIV-1 activity. A phenylazo-naphthalene sulfonic acid derivative, designated ADS-J1, was found to inhibit both formation of NC-1 detectable complex and HIV-1-mediated membrane fusion, suggesting that the described ELISA is applicable to rapid screening of libraries of organic compounds for HIV-1 inhibitors targeted to the HIV-1 gp41 core structure.