The gene frequencies of nine different genetic polymorphic markers [ABO, MNS and P blood groups; haptoglobin, transferrin, Gc protein, complement (C3), properdin factor B and α1-antitrypsin] were determined in 94 Mexican-Americans residing in the Los Angeles, California area. Comparisons with published data on Mexican-Americans living in other areas of the United States or in Mexico itself revealed no significant differences in the gene frequencies between this and previous studies. However, data from the current study demonstrated significant differences in ABO and haptoglobin allele frequencies compared to published non-Hispanic Caucasian data. These data suggest a large degree of genetic homogeneity in the Mexican-American population residing in the United States. Additional gene marker studies will be important to test this hypothesis and further define the degree of non-Hispanic Caucasian admixture in this population