The delta F508 mutation and cystic fibrosis (CF) haplotypes with the markers KM19, pMP6d-9 and J3.11 are described in 54 adult British CF patients. delta F508 was found on 70% of all CF chromosomes, on none of the normal chromosomes and on only 37.5% of pancreatic sufficient CF chromosomes. All patients with meconium ileus were homozygous for the deletion.