A total of 977 White individuals living in five Brazilian cities, as well as 173 Black individuals from two of these cities have been studied in relation to HLA-A and HLA-B. Allele frequency similarities among these populations are much more impressive than dissimilarities, and the differences, considering putative ancestors, are not remarkable. This limited variability can be only partially explained in terms of racial admixture, estimates of the latter using different alleles in the various populations showing disparate results. Linkage disequilibrium values vary between groups, that for A1-B8 being the most consistent, independent of sample or race. But four other haplotypes observed to be in significant disequilibrium in Portugal showed the same pattern in at least one of the five Brazilian White samples.