The hybridization of DNA oligomers including molecular beacons can be detected by measurement of either the decay time or the intensity of a single fluorescent label attached to the end of the respective oligonucleotide. The method works both in solution and solid phase and can distinguish between fully complementary and mismatch sequences as demonstrated for a 15-mer oligonucleotide and a 25-mer molecular beacon. The fluorescence lifetime method is advantageous in (a) requiring a single label (and therefore a single labeling step) only; and (b), being based on measurement of a self-referenced magnitude that is hardly affected by parameters such as fluctuations in light intensity that make measurement of intensity more prone to interferences.