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Allele frequencies for the ABO, Rh, MNSs, Duffy, Kidd, Lutheran, P and Lewis blood group systems in 207 persons whose 4 grandparents were born in the Monterrey Metropolitan area (MMA), grouped into 3 generations, were ascertained along with other related population from the MMA, Mestizos from Saltillo, Coahuila and Tlaxcala, and from the populations thought to have contributed to their genetic constitution (native Mexican Indians and Spanish). Genetic admixture and distance estimates were calculated. Gene frequencies of the three generations from MMA are intermediate to those of the ancestral populations, indicating that they are Mestizo but with a genetic structure different from Mestizos of Saltillo and Tlaxcala. Both genetic admixture and distance estimates indicate that the oldest generation exhibits the greatest Spanish influence which decreases in the youngest generation and in the other MMA populations as a result of the immigration from the central states of Mexico.