Data on RFLP analysis of the phenylalanine hydroxilase (PAH) locus in phenylketonuria (PKU) patients, their parents, and healthy donors from four ethnic groups of Bashkortostan are presented. Forty-one probands were examined; seven and 7 R408W homozygotes and 16 compound heterozygotes carrying one parental chromosome with the R408W mutation and the other chromosome with an unidentified mutation were detected. The R408W mutation was found to account for only 38% of PKU chromosomes in Bashkortostan. Analysis of the frequency distribution of MspI (Aa) polymorphic alleles of the PAH gene showed that the frequency of the A allele in the populations studied varied from 0.38 to 0.49, and its distribution was similar to that found in the populations of Europe and western Russia. Examination of MspI genotypes revealed statistically significant differences in the distribution of Aa alleles among PKU patients and healthy individuals from Bashkortostan, with the a allele being was more common in the group patients, where its frequency was estimated as 0.84.