Cystic Fibrosis (CF) is an autosomal recessive hereditary disease, caused by the defect of a membrane transport protein. The defect is due to the mutation of the gene coding this protein. To date, these mutations have been analysed by direct mutational analyses in prenatal diagnosis. During gene sequencing, intragenic polymorphic markers (microsatellites) were identified, enabling the indirect analysis of the mutant allele. The markers characterize the given allele, so that the inheritance according to the Mendelian rules could be followed. We introduced a DNA-diagnostic method based on the amplification of three intragenic microsatellites. This new and efficient prenatal diagnostic tool would provide more reliable test results for previously screened CF families, in which direct mutation analysis was not informative.