The kinetics of opening of the DNA quadruplex formed by the human telomeric repeat havebeen investigated using real-time fluorescence resonance energy transfer (FRET) measurements with apeptide nucleic acid (PNA) trap. It has been found that this opening is zero-order with respect to PNA,indicating that the initial step is a rate-limiting internal rearrangement of the quadruplex. A study of thetemperature dependence of the rate of quadruplex opening was performed and the activation energy ofthe process estimated to be 98 ± 8 kJ mol-1.