We have used cloned DNA sequences from the 5' end of the met locus and the D7S8 locus to locate new restriction fragment length polymorphisms. TaqI and MspI polymorphisms with frequencies of 0.34/0.66 and 0.10/0.90, respectively, for met and a PvuII polymorphism (0.15/0.85) at D7S8 are described. We used these new markers to analyze our reference panel of cystic fibrosis pedigrees and found that they provided additional information in several families. No evidence for recombination was observed between the 5' end of met and previously described met markers. We present examples of the use of the met markers in the clinical diagnosis of cystic fibrosis and summarize our analysis of 29 clinical cases including eight prenatal diagnoses. We conclude that DNA-based prediction of cystic fibrosis is an effective clinical diagnostic procedure.