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Unrelated individuals from 3 relatively isolated Africanderived communities in the state of Piaui, northeastern Brazil, and blood donors from Teresina (admixed population), the capital city of Piauf, were analyzed for the ESD, CA2, GC, HP, GLOl, PGM1, HB, ACPI protein loci and for the VWF1 and VWF2 short tandem repeat (STR) loci. As expected, high frequencies of alleles considered characteristic of African populations were detected. The VWF1 allele distribution was bimodal, whereas the VWF2 distribution was unimodal, suggesting differential action of mutation and selection factors in the 2 STRs despite their close location on the same gene. The genetic distances between the Brazilian isolates coincide with their geographic distances. The ethnic admixture estimated by a maximum-likelihood method showed African, European, and Amerindian components of 61%, 17%, and 22% for Mimbo, 72%, 12%, and 16% for Sitio Velho, and 31%, 21%, and 48% for Teresina, respectively.