A novel method for detection of any mutation located within a PCR-amplified DNA sequence was demonstrated. The method is based on the inhibition of spontaneous DNA branch migration. Partial duplexes produced by PCR amplification of a test and a reference genomic DNA sample anneal to form four-stranded cruciform structures. Spontaneous DNA branch migration results in dissociation of these structures when the test and reference sequences are identical. Any base substitution, deletion or insertion inhibits branch migration and produces stable cruciform structures. When suitable ligands are attached to the PCR primers, the cruciform structures can be detected by standard immunochemical methods. This approach was tested using several commonly occurring mutations within the human cystic fibrosis gene. New methods for increasing the specificity of PCR amplifications are described that were used for successful mutation analysis.