Cystic fibrosis (CF) is an inherited, recessive disease that primarily affects the pancreas of the digestive system and the lungs of the respiratory system. The disease is caused by mutations in the gene encoding the CFTR (Cystic Fibrosis Transmembrane conductance Regulator) protein. When the protein is defective, it causes the body to produce thick mucous that clogs the lungs leading to infection, and the pancreas is blocked, stopping the digestive enzymes from reaching the intestines where they are required to digest the food. So far, more than 1400 mutations have been identified in the CFTR gene. The most common mutation is the p.F508del mutation (hereafter called ÄF508), which occur in about 70% of the patients. The severity of the disease varies according to which mutations the patient has inherited. Two patients with identical mutations can however display very different symptoms of the disease. This is because the disease is greatly influenced by environmental factors and genetic factors other than CFTR.The fatty acid metabolism has been shown to be abnormal in patients with cystic fibrosis, as they have altered levels of plasma fatty acids caused by a deficiency of essential fatty acids. In this project, we wanted to investigate whether the abnormal metabolism of fatty acids in CF patients could be due to a change in the uptake of fatty acids from the intestine. We wanted to see if we could find an association between CF and markers (di-nucleotide repeats) close to the genes (SLC27A 1-6) encoding the six known fatty acid transport proteins; FATPs 1-6. We have used DNA from 40 CF patients homozygous for the ÄF508 mutation. For comparison, we included material from 145 blood donors, negative for ÄF508. The D9S164 marker (close to SLC27A4) gave an interesting result in the statistical tests. We therefore included two additional markers closer to the gene encoding FATP4, but these came out negative, and possibly made the positive result for D9S164 less relevant. A polymorphism, Gly209ser, was previously tested on a group of healthy middle-aged men in Sweden. Men heterozygous for this polymorphism were shown to have a lower BMI compared to those homozygous for the polymorphism, and the condition was found to be associated with insulin resistance. Incidence of diabetes in CF patients increases with age, and CF patients often have BMIs below the average. These facts together with the weak association of D9S164 to FATP4 made us test the subjects and the normal controls for the Gly209Ser polymorphism in SLC27A4. The normal controls had an allele frequency of Gly = 0.945 and Ser = 0.055, the CF patients, however, all came out homozygous for the normal variant (Gly = 1.00, Ser = 0.00). The hypothesis that CF patients would show a higher allele frequency of Ser compared to the normal controls was therefore not confirmed. These studies have not given any conclusive results, and further studies should involve the use of a larger set of CF-patients.