Using a chimeric primer consisting of the nucleotide sequence derived from the HIV-1 envelope gene coding for the second conserved region of gp120, and the highly conserved sequence derived from the human immunoglobulin gene coding for the VHIII domain, it has been identified in sera of AIDS patients HIV-1 field isolates carrying the complete and active Chi recombination hot spot (GCTGGTGG). The recombination between the HIV-1 gene coding for the central portion of gp120 and the bacterial gene coding for the clp protease was also demonstrated in vivo. These results point out serious concern that vectored AIDS vaccine candidates carrying the HIV-1 env gene on viral and bacterial vectors could become the source of potentially new infectious diseases rather than an effective instrument for AIDS prevention.