The importance of chemokine receptors in the pathophysiology of HIV infection became apparent when it was demonstrated that persons at high risk for HIV-1 infection remain uninfected when they carry a polymorphic variant of CCR5. In individuals who are homozygous for the 32 base-pair deletion in the CCR5 gene, a functional protein cannot be synthesized and such persons are not found in HIV-1 positive cohorts. Furthermore, in individuals heterozygous for that mutation, there is an association with slow disease progression. The mutant allele of CCR-5 is present at high frequency in the Caucasian population, but is absent in the Japanese and black populations. The aim of this study was to assess the frequency of the truncated allele of CCR-5 gene in the cohort of HIV infected and non-infected subjects in the Province of Chaco, Argentina (with Guaraní and Hispanic genetic background). A total of 118 unrelated seronegative healthy blood donors and 80 seropositive HIV-1 subjects were studied. A portion of CCR-5 gene from genomic DNA was amplified by PCR and analyzed on a 3% agarose gel. The frequency of the delta CCR-5 allele was 2.5% for homozygous and 15.3% for heterozygous seronegative subjects, similar to that reported in the Caucasian population; the homozygous CCR-5 allele was absent in HIV-1 positive patients and the frequency of heterozygous was 2.5%, significantly lower than reported in the Caucasian population.