In a procedure known as diathermy, high-tech doctors use electrical currents, ultrasonic waves, or microwave radiation to boost the temperature at selected points in the body. They may also resort to extracorporeal heating, removing blood from the body, heating it, and returning it to the body at a higher temperature--a procedure that has been used in the battle against human immunodeficiency virus (HIV). To get any of these treatments, you'll probably need to check into a medical center.

Natural healing practitioners, on the other hand, tend to favor less exotic forms of treatment that can be given on an outpatient basis in the office or clinic. The equipment required is typically nothing more than a bathtub, sauna, or steam room.

Whole-body immersion is an especially common approach. It's usually done in a deep, stainless steel tub. The water is typically heated to between 101 and 108 degrees Fahrenheit, although temperatures as high as 115 degrees are sometimes used if the patient can tolerate them. The goal is to keep the body temperature at between 102 degrees and 104 degrees Fahrenheit for about 20 minutes.

Locally-applied hyperthermia may also be used, for example in the treatment of a hand or foot wound, and many practitioners use a combination of hyperthermia and cold baths or compresses to help stimulate circulation. For example, one leading hyperthermia clinic, the Uchee Pines Institute, employs the following treatments for headaches:

• Hot foot bath with cold compresses to the head.
• Alternate hot/cold foot bath (three minutes hot, thirty seconds ice water) and cold compresses to the head.
• Alternate hot/cold applications to the head, starting with hot compresses at the base of the head and ice water compresses at the face, temples, ears and forehead. After three minutes, the areas of heat and cold are switched; the complete cycle is repeated two more times.

   Although treatments often amount to little more than sitting in a very hot tub, do-it-yourself hyperthermia is not recommended due to the extremely high temperatures required.

Treatment Time: For whole-body immersion, a typical treatment requires approximately 30 minutes--10 minutes while the body temperature rises and 20 minutes while the high temperature is maintained. The time required for other forms of treatment varies widely.

Treatment Frequency: The course of treatment depends on your problem and the type of therapy. For upper and lower respiratory infections, patients typically undergo only 1 or 2 treatments. For more serious conditions, however, therapy can take much longer. Cancer patients typically begin with 15 treatments over a 3-week period followed by a 3-week rest. The cycle is then repeated 4 more times.

Other, more intensive hyperthermia treatments are used to treat viral infections. For example, much research has been done recently on the use of hyperthermia in the treatment of HIV infections. Some studies have shown that HIV is temperature-sensitive and becomes much less active at temperatures above 98.6 degrees Fahrenheit.

In the treatment of cancer, some studies have shown that hyperthermia can modify cell membranes in a manner that actually protects the healthy cells and makes the cancer cells more susceptible to chemotherapy and radiation treatments. Used as an adjunct, hyperthermia may thus permit lower doses of these potent and toxic forms of therapy.

Much research is also being conducted on hyperthermia's beneficial effect on the immune system. Researchers have found that although the white cell count appears to drop immediately following hyperthermia treatment, it rebounds strongly within a few hours. Furthermore, the cells' ability to destroy invaders appears to be enhanced.

Among many natural healing practitioners, hyperthermia is also viewed as a means of ridding the body of toxins such as pesticides, food additives, and other chemicals thought to disrupt the immune system. There is currently no evidence that it works in this manner.

A number of other conditions can increase your sensitivity to extreme temperatures. If you have anemia, heart disease, diabetes, a thyroid problem, a seizure disorder, or tuberculosis, you may need to either reduce the number of treatments you take, exercise more precautions, or, perhaps seek another method of treatment altogether. Before beginning the treatments, you should also give the doctor a list of all the medications you're taking. High temperatures can increase the impact of certain drugs--theophylline, for example--to the point where they become toxic.

Keep in mind, also, that those seeking this type of treatment for an acute illness such as pneumonia may have a more difficult time tolerating extreme temperatures at the outset. The treatments can also cause a temporary flare-up of some chronic conditions such as herpes. However, these initial side effects may subside after a fever is initiated.

As when choosing any physician or therapist, it's important to ask questions regarding the length of treatment, expected outcomes, and side effects. The doctor should be able to give you specific answers in all of these areas, as well as information related to your unique situation and state of health.