Mutations in genes encoding the keratin intermediate filaments expressed in basal cells have been identified in some families with epidermolysis bullosa simplex as the proximate cause of the fragility. We have systematically scanned genomic sequences of one of these keratins, keratin 14, for mutations in patients from 49 apparently independent kindreds using single-strand conformation polymorphism analysis. The ten mutations identified are clustered at three sites--the ends of the helices and the L12 linker region, mutation sites that have been identified in past, more limited studies. Early onset of blistering in these ten families is correlated with more widespread distribution of lesions.