Data are presented for delta F508 screening and KM19/XV2c haplotype analysis of 195 cystic fibrosis (CF) chromosomes from the British Caucasian population. We report the frequency of delta F508 in this group to be 80% and find pronounced disequilibrium between the deletion and the KM 2, XV 1 haplotype. Haplotype analysis of 71 normal chromosomes is also presented. We report one individual who had meconium ileus and who does not have the delta F508 mutation on either chromosome.