The term radiological hyperthermia is used to describe the exposure of biological tissues to temperatures just above physiological ones, namely between 42 and 45 degrees C. A machine for hyperthermia (SAPIC SV03 produced by Aeritalia, Caselle, Turin) is been experimentally used at the authors' institute. The present study aims to analyse the technical and qualitative aspects of temperature control using invasive and previsional thermometry. The term invasive thermometry is used to describe the insertion of small teflon catheters into the biological body through which thermometric probes are introduced to control deep temperature. Previsional thermometry is the phrase used to describe the computer simulation of hyperthermic treatment, starting from knowledge of the tissue to be heated and the type of applicator used. The simulated treatment and the real temperature measured are then compared in order to optimize the treatment used.