PTCH, the human homologue of the Drosophila segment polarity gene, patched, has been identified as the gene responsible for Gorlin or nevoid basal cell carcinoma syndrome (NBCCS). We report here the characterization of four novel mutations in the human PTCH gene in germ-line DNA from Gorlin patients. All mutations lead to truncation of the predicted protein product. Also included is a list of putative polymorphic nucleotide postions in the sequence covered by published primers.