The presence or absence of the major cystic fibrosis (CF) mutation, delta F508, in the general patient population was determined by Kerem et al. using allele-specific oligonucleotides for the mutant and normal sequences in the polymerase chain reaction (PCR). delta F508 was identified by Riordan et al., and it is a 3-bp deletion of the phenylalanine codon at position 508. The Hutterite Brethren are an inbred North American population who have three different DNA marker haplotypes of CF chromosomes. Genomic DNA from both a CF child and one parent from each of 10 Hutterite families was analyzed for the presence or absence of the deletion mutation. delta F508 is associated with one of the three CF haplotypes in the Hutterite population, and this is the most common haplotype in a subset of the linkage family data of Kerem et al. The other two Hutterite CF haplotypes are generally rate in Caucasian populations. Since these two CF haplotypes do not carry the deletion mutation, they must carry a different CF mutation(s). The results of the PCR analysis for the deletion mutation lend additional support to our previous conclusion that there were at least three original carriers of CF mutations among the founders of the Hutterite population and that all copies of the same CF haplotype were identical by descent. One Hutterite CF patient has both of the haplotypes which do not carry delta F508. Analysis of this individual's DNA should allow identification of two additional CF mutations in this population.