In a study utilizinga peptide library derived from human hemofiltrateto search for new inhibitors of CXCR4-tropic HIV-1 infection, an endogenousantagonist of CXCR4, termed endogenous peptide inhibitor of CXCR4(EPI-X4), was discovered (Table 1).22,23 EPI-X4 is a 16-mer fragment ofhuman serum albumin that specifically binds to CXCR4. The gene discussed is CXCR4; the disease is HIV-1 infection.