The narrow spectrum of HIV-specific neutralizing anti- bodies points to the need for new immunogens based on highly conserved epitopes. HIV-1 infects host cells by membrane fusion: during this process conserved epitopes are exposed on the viral glycoprotein gp120/41 that may be used as targets for the induction of antibodies against HIV-1. Neutralizing antibodies against different heterolo- gous HIV-1 isolates may be obtained by immunizing mice with fusion complexes on which conserved epitopes have been stabilized by fixation, or with gp120/41s with a CD4-independent phenotype on which these conserved epitopes may be already exposed.