A sample of 165 patients who were inhabitants of Russia was screened for seven CFTR gene mutations, and analysis of polymorphism frequency at two marker loci (KM19 and VNTR in intron 6 of the CFTR gene) was performed in normal and mutant chromosomes. The frequencies of mutations in 330 mutant chromosomes were distributed as follows: delta F508, 57.5%; G542X, 1.07%; and R33AW, 0.45%. Mutations G551D, R553X, R347P, and 1154insTC were not found. Alleles and haplotypes of KM19 and VNTR loci in intron 6 of the CFTR gene were characterized by a marked linkage disequilibrium with the CFTR gene. Haplotype 2-6 showed an absolute linkage disequilibrium with the delta F508 mutation.