Samples and DNA analysis. DNA samples from 66 unrelated CF patients were studied. All these patients come from northern Greece (Thrace, Macedonia and Thessaly) and attend the Cystic Fibrosis Unit of the Hippokration General Hospital of Thessaloniki, Thessaloniki, Greece. The geographical origin of the patients was established by assessing the birthplace of each of the patient's parents and grandparents. They were diagnosed by a positive sweat test and typical clinical findings. Genomic DNA was extracted from whole blood by the phenol-chloroform protocol. The DF508 mutation was detected by polymerase chain reaction (PCR) followed by polyacrylamide gel electrophoresis (PAGE). Detection of mutations G551D, R553X, W1282X, N1303K, 621+1 (G®T), R334W, 1717–1 (G®A) and E822X [6-12] was carried out by using specific digestion of the PCR products with restriction enzymes (New England Biolabs, Inc., Boston, MA USA).