Blood samples were obtained from the Department of Pediatrics at the Children’s Hospital, Zagreb, Croatia. The diagnoses were based on clinical presentation and positive sweat Cl^– test (over 60 mmol/L). Genomic DNA was isolated by a standard salting out procedure [5]. The mutations were detected by heteroduplex analysis and restriction fragment length polymorphism (RFLP) [6,7]. The polymorphisms were detected by denaturing gradient gel electrophoresis (DGGE) [8].