Cystic fibrosis (CF) is the most common autosomal recessive genetic disorder amongst populations of northern European descent. Cloning of the cystic fibrosis transmembrane regulator (CFTR) gene in 19891 has allowed the assessment of clinical phenotype in patients with a specific genetic abnormality. Genotype/phenotype analysis showed a good correlation between the common CF mutation (deletion of phenylalanine at position 508 in the CFTR gene) and pancreatic insufficiency. This correlation does not hold for pulmonary disease which can vary markedly between patients with the same ΔF508 CFTR mutation.2 Many explanations have been advanced to account for this finding. Pulmonary disease is influenced by environmental factors such as the patient's age, pancreatic status, treatment regime, social class, smoking history, nutritional status, and colonisation with strains of Pseudomonas aeruginosa or Burkholderia cepacia.3-8 Moreover, …