Monica U, age 13, of Hopewell, Va., for her question:

EXACTLY WHAT IS ACUPUNCTURE?

While the Egyptians are given credit for first developing a medical science, the Chinese were also very early practitioners of caring for the ailing members of their society. From the most ancient days of civilized man, the Chinese were developing their own special ways of dealing with health and the maintenance of sound bodies.

One of the most ancient medical practices was the Chinese method of relieving pain and treating diseases by inserting needles into various parts of the body. The system was called acupuncture.

Acupuncture does indeed seem to work, although scientists are unable to give us a clear explanation of why it works and exactly how good results are accomplished.

The Chinese have a special doctrine that says the body must receive two special vital principles, or ''humors.'' The two are called yin and yang. Many diseases, it is believed, result from the obstruction of the supply of yin and yang. If the balance between the two is not maintained, a person will become ill.

Acupuncture is believed to improve this balance. Many Chinese doctors believe that acupuncture actually changes the flow of a mysterious life force in the body. They describe this force as flowing within 12 meridians.

The acupuncture procedure calls for the insertion into the body of silver, gold or steel needles. Each needle can be between one and 10 inches long. There are about 65 places on the body, mapped out by the doctors, where the needles can be inserted. By placing the needles into specific parts of the body, certain benefits are obtained. The needles may be either hot or cold.

Acupuncture has been effectively used to relieve the pain of and to treat such conditions as arthritis, asthma, migraine, ulcers, poor eyesight and even some types of mental illness.

Since the 1960s, doctors in China have been performing major surgical operations with acupuncture as the only anesthetic. The patients, during these surgeries, have been conscious and apparently have felt little or no pain.

Many doctors in most of the countries in the Far East and Southeast Asia use acupuncture. It has also been used successfully during recent years in England, Germany, France and Russia.

During the 1970s, a number of physicians in the United States and Canada have been studying acupuncture in an effort to learn more about it. They want to know just why and how certain effects are obtained.