Conditions for assessing KM-19 probe detected by Pst-1 restriction fragment length polymorphism (RFLP) by means of polymerase chain reaction were provided. Computer controlled mechanical arm with waterbaths and cloned heat-stable DNA polymerase was used. Results of KM-19 allelic frequencies on 90 cystic fibrosis chromosomes are presented. Allele two frequency was -0.833.