A method for detecting the presence of a target nucleic acid sequence in a sample, said method comprising: performing nucleic acid amplification on the sample in the presence of (a) a DNA duplex binding agent, (b) a nucleic acid polymerase and (c) a reagent comprising an amplification primer which can hybridize to said target sequence when in single stranded form and which is connected at its 5' end to a probe which carries a label by way of a chemical linking group, said labeled probe being of a sequence which is similar to that of the said target nucleic acid sequence, such that it can hybridize to a complementary region in an amplification product, and wherein the label is able to absorb fluorescence from or donate fluorescent energy to the DNA duplex binding agent; and monitoring fluorescence of said sample.