An instrument is proposed for noninvasive mapping of internal body temperatures during hyperthermia cancer therapy. This instrument may provide a means to control the temperature and distribution of heat applied by microwave or applied by heating ultrasound radiation. The instrument relies upon the temperature dependent speed of ultrasound in tissues, from which temperature may be reconstructed by tomographic techniques. Accurate calibration will be assured by including one or more of the latest available invasive point temperature probes within the instrument's field of view. Evaluation of the method will involve laboratory tests on artificial models, phantoms, and excised tissue samples, after which the prototype instrument will be evaluated using animals (such as young pigs) and, perhaps later, volunteer humans. Further tests will be conducted on a second generation scanner designed for imaging more difficult parts of the body such as the limbs, the neck, and the abdomen, where bone or gas may limit the field of view or cause troublesome reflection or refraction.