Abstract: The invention relates to a device for the amplification of DNA in a reaction mixture, the device (1) comprising a heated chamber (2) including a rotor (3) for holding a plurality of reaction vessels for reaction mixtures, a drive means for the rotor, a microwave energy source (8) with means for controlled delivery of said energy to the reaction mixtures, and a system (14-16) for determining denaturation of double-stranded DNA. The invention also provides a method for the amplification of a nucleic acid strand. In the first step of the method, a reaction mixture is formed comprising the target nucleic acid strand, nucleotides, a primer, a thermostable nucleic acid polymerase, and, if necessary, a reagent for the detection of denaturation of double-stranded DNA. In the second step, the mixture is incubated at a temperature which allows synthesis of a nucleic acid strand complementary to the target nucleic acid strand.