We have designed a study aimed at identifying the genetic mutations responsible for cystic fibrosis (CF) in the population of the United Arab Emirates. The prevalence of CF in the UAE is at least 1/15,000 live births and the disease is associated with very severe clinical presentations. We have investigated 17 unrelated families. Ten UAE national families were of Bedouin descent: all 15 CF patients, who presented with very severe forms of the disease, were homozygous for a S549R mutation due to a T->G transversion at nucleotide postion 1779. Amongst a distinct population of Baluch origin, CF patients from 6 out of 7 affected families were DF508 homozyotes. Hence, the unique distribution of CF mutations in the United Arab Emirates--two mutations, S549R and DF508, characterize so far 94% of CF families--should allow efficient organizing and delivering of CF carrier screening programmes on the country's relatively limited population size.