A method of detecting a target nucleotide sequence in a nucleic acid molecule, which comprises: (a) binding of an oligonucleotide probe to said nucleic acid molecule; (b) selective labelling of the bound oligonucleotide probe in the presence of said target nucleotide sequence; (c) hybridisation of the labelled oligonucleotide to a complementary sequence; and (d) subsequent detection of the label; such methods being suitable for qualitative and quantitative assays of microbiological populations.
