Background: The Parakana is a group of Indians with cultural similarities to the extinct Tupi group. They are an isolated native population from East Brazilian Amazon. A number of different O alleles have been found at the blood group ABO locus in populations of several ethnic origins (Caucasians, Blacks, Amerindians). Aim: The present study describes the ABO blood group polymorphism gene of the Parakana Indians. The Amerindian group was carefully selected for racial background. Subject and methods: The blood group polymorphism was analysed in genomic DNA from 62 Parakana Indians. We determined the 261G deletion, the T646A and C771T mutations described in O-1variant and the G542A substitution, using PCR-RFLP (polymerase chain reaction-restriction fragment length polymorphism). Results: All Amerindians studied were homozygous for the 261G deletion. The frequencies of the T646A and C771T mutations in Parakanas (0.65) were lower than that observed in Kayapo, Yanomama and Arara Indians (0.91) (chi(2) = 18.24; p-nu<0.001. The G542A substitution in Parakanas was also lower (0.22) than in other tribes (0.42) (&chi;(2)=9.73; p-&nu;=0.001). Conclusions: The different O alleles including the G542A mutation are not distributed homogeneously among all Amazonian Amerindians. Our results are in agreement with other genetic markers studied previously in Parakana Indians, whose distinct genetic pattern differs from Europeans and even from other Amerindians.302220224