The gene causing adenomatous polyposis coli (APC) has recently been cloned. Three intragenic polymorphisms were reported to be detectable by single-strand conformation polymorphism analysis. Here, we describe an assay using polymerase-chain-reaction-based amplification and subsequent enzymatic digestion of genomic sequences to identify polymorphic sites at nucleotide positions 1458 and 5037 of the APC gene.