Ultrasound and diathermy are used as heat therapy modalities, and their effectiveness in producing the physiological reactions characteristic of a heat mo-dality is also directly related to the temperature rises they produce. In the case of ultrasound, temperature rises in the forearm3'4 or in the thigh5 are typically 1.8 to 3.6°F (1°C-2°C). At a depth of 0 to 2.38 cm, microwave diathermy at 2,456 Mc produces rises of 3.6°F (2°C) in the thigh6 and similar rises in the forearm muscles.7,8