The allele frequency of GATT and Mp6D-9 markers was investigated in 32 cystic fibrosis (CF) families. The GATT6 allele was found to be significantly associated with the delta F508 mutation. The Mp6D-9 allele 2/GATT6 haplotype was the major haplotype of the mutant alleles. Further analysis of CF alleles for population-specific mutations is underway so that a more direct approach can be taken, especially for families seeking prenatal diagnosis.