Summary Human aconitase (ACNO 8 ) polymorphism was studied in three samples from northeastern Brazil. Two of the samples were collected in the State of Bahia and one in the State of Sergipe. The main characteristic of the samples was given by different degrees of Black admixture. The results showed that the more negroid the saniples the higher the frequencies of the alleles ACNO 4 8 and ACNO 6 8 . These findings fit well with the known ACON s gene frequencies in prcmnt‐day Siperians and with the past history of Yoruba slaves in Bahia.