Abstract: A labeled nucleic acid probe comprising a single-stranded oligonucleotide probe having a nucleic acid sequence complementary to a specific nucleic acid sequence in a target nucleic acid and an intercalating fluorochrome bound to said probe is used to detect the target nucleic acid by a convenient, single-stage method in a homogeneous system. The formation of a complementary bond between the probe and the target nucleic acid can be detected and the amount of the resulting complementary binding product determined without requiring any extra step such as for removing the excess probe which has not participated in the complementary binding.