Seven genetic systems were used to investigate the racial composition of a sample from a low-income Mexico City Mestizo group, finding estimates of 0.590, 0.348, and 0.062 of Indian, White, and Black ancestry, respectively. The results are similar to another Mexico City group studied previously and to several Mestizo populations from different parts of the country. The one thing in common in all these groups is low socioeconomic status. There is only one report suggesting that Mexico City Mestizos have around 70% White ancestry, and there is reason to believe the sample was taken from a high socioeconomic group. It is suggested that low socioeconomic Mexican Mestizo groups are characterized by a high Indian ancestry, above 50%. © 1995 Wiley-Liss, Inc.