A method to identify a specific oligonucleotide sequence without use of radiochemicals, electrophoresis or centrifugation. An oligonucleotide biotinylated at its 5'-end and another with a reporter group (chromophore or fluorophore) at its 3'-end are constructed to hybridise to the sequence to be detected in a template DNA strand. A ligase is able to join the two oligonucleotides if they both match the template perfectly. The ligated oligonucleotide can be extracted from the mixture on to immobilised streptavidin and the presence of the reporter group detected.