The Thermal Diffusion Probe (TDP) System allows continuous real-time measurement of tissue perfusion in flaps. The authors used a TDP with two thermistors, one active, the other passive, embedded in a 0.9-mm diameter catheter to measure continuous tissue perfusion in rabbit epigastric flaps. The distal thermistor is heated to 2 degrees C above the tissue baseline temperature. The power required to maintain this temperature difference is mathematically related to the tissue perfusion in the volume surrounding the probe tip. Central and peripheral TDPs were placed. The TDP effectiveness in detecting and measuring daily tissue perfusion in buried epigastric flaps was tested. Contralateral epigastric pedicles were transposed into the flaps prior to ligation of the original pedicle. Flaps with transposed pedicles showed a progressive and significant increase in tissue perfusion during the initial 3 weeks of the experiment, compared to flaps without the pedicle transfer. The TDP System is a useful experimental method for the continuous and real-time quantification of flap perfusion and may be helpful in making clinical decisions about prefabricated flap transfer.