Radiofrequency (RF) radiation between frequencies of 1 MHz and 100 GHz is, to varying degrees, readily transmitted and absorbed in biological tissues. Because of its internal absorption characteristics, RF radiation in the microwave spectrum (300-10,000 MHz) has been used in cases where a rapid rate of warming is desired without raising actual temperature beyond lethal levels. For example, microwave exposure has been used to quickly thaw canine kidneys, warm human blood from 4 to 37 C in 1 min, and selectively warm the cardiac area of hypothermic rats. It is conceivable that whole-body exposure to RF radiation could be used in the rewarming of subjects in experimental or accidental hypothermia. Warm-water baths have conventionally been used for rewarming hypothermic individuals, however, this method is relatively slow and can lead to ill effects such as hypoglycemia and reductions in arterial blood pressure.