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Surnames were studied in two Brazilian samples: one from Manaus, capital of the state of Amazon, and the other from Lengois, a city in the hinterland of the state of Bahia. In the sample from Manaus, surnames were used to assess the effect of Black and American Indian admixture on the gene frequency distribution of alcohol dehydrogenase (ADH3) in 300 newborns. The results confirm the previous findings of a lower ADI23 allele frequency in Blacks and suggest that American Indians have an ADH23 allele frequency similar to that of local Whites in Amazon.In the sample from Lengois, surnames were used in addition to racial classification, for a historical reconstruction of the racial admixture in the city since 1890.The results show an admixture trend towards a less Black and more White popula­tion. The evidence for this is an absolute growth in the proportion of Whites, and an increase in the frequency of devotional surnames within Whites, meaning that there is a growing proportion of Black descendants becoming classifiable as White.