Abstract: A method of measuring the temperature of the core of a body includes: a) providing a heat conductive space outside the body and in contact with its surface; b) monitoring the difference of the temperatures of two points located within the space and at different distances from the body surface; c) if the temperature difference indicates that heat is flowing from the body surface outwards, generating heat in the space in order to reduce the temperature difference; d) monitoring the temperature difference; and e) assuming the temperature of one of the two points, when the temperature difference is zero, as the temperature of body core.