A search for antigens of the HLA system has been carried out in 53 Mataco Indians of Argentina living in a geographically isolated area in the northeast of the country. Samples were mostly collected from adults of both sexes who were not directly related.Lymphocyte typing was performed using the microcytotoxicity technique of NIH. 118 sera specific for 15 antigens of the first HLA locus, 22 antigens of the second and 6 of the third were used.The most frequently found alleles were HLA‐A28, Aw31 and A2 for the first locus; B15 and B40 for the second; and Cw3 and Cw4 for the third.In addition to previously published investigations on South American Indians, our typing work shows a remarkable homogeneous gene pool and a restricted range of polymorphism; therefore, a further set of haplotypes rendered us also restricted. The most frequent haplotypes that showed a significant statistical linkage desequilibrium were: A2‐Cw4, A28‐Bx, A2‐Cw3, Aw31‐Bw16, Aw24‐Cw3, B15‐Cw3, Bw16‐Cw3 and A28‐B5.Some of these haplotypes have also been found in other i