Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, that encompasses 250 kb of genomic DNA, cause cystic fibrosis. More than 5-10% of CF patients in most populations studied carry undefined mutations and hence intragenic CA repeats are important tools in genetic counselling. To date, polymorphic intragenic repeats have been found in introns 6a, 8 and 17b. We have identified a novel CA repeat within intron 1 of the CFTR gene that lies about 70 kb 5’ to intron 6a and so will be a useful additional diagnostic marke