A group of 42 cystic fibrosis (CF) patients and 80 heterozygote carriers was analysed for determining the prevalent CF haplotypes and the frequency of delta F508. The "high-risk" haplotype B (XV2c-KM19/1 2) was found in 66% of CF chromosomes. The prevalent normal haplotypes were A (1 1) and B (2 1). The deletion was detected in 54 CF chromosomes (56%), homozygotes constituting 35% of all CF patients. In 88% of cases the mutation was linked to haplotype B, and in 12% to haplotype D (2 2). Chromosomes that did not have delta F508 were found to be evenly distributed among all four XV2c-KM19 haplotypes. The use of restriction fragment length polymorphisms and direct detection of the mutation makes 94% of CF families fully informative for prenatal analysis.