Due to the proximity of the indwelling thermometer to the surface of the body, the temperature does not reflect the real core body temperature and preliminary data, taking by our group, suggest a significant, but stable difference between core body temperatures measured with an indigestible device, compared to the temperature taken with the rectal probe. WBH treatments, currently studied by our group at the University of Arizona, are of mild nature and the constant infra-red heating is stopped, as soon as a patient reaches the rectal temperature of 38.5 C. Due to the fact, that the bodies surface is heated up through the infrared exposure, the investigators assume, that the core body temperature will be lower, compared to the rectal temperature. A validation study in 20 subjects therefore is necessary to determine the differences in the measuring methods. This is especially important, as the end-point of the treatments is defined by the core body temperature, and different endpoints by switching from one measuring method to the other, without validation, would potentially bias the study results.