Q. Three years ago I had my prostate removed because of a small cancerous growth. Since that time I have had regular examinations, including blood tests for acid phosphatase, and all has been normal. My urologist assures me that if a cancer grew anywhere in the body, the acid phosphatase test would indicate that. My regular physician, however, says that this would not be the case. Who is right?

A. If the level of acid phosphatase in your blood were high, it would suggest that the cancer had returned. However, it is possible for the cancer to come back, especially early on, without raising your acid phosphatase test.

Acid phosphatase is an enzyme found mainly in the prostate gland. High levels of this enzyme are produced in some cases of prostate cancer and benign prostate disease, but they can occasionally occur in other conditions including some bone and liver diseases.

This test is not good enough to screen for prostate cancer, the second most common cancer in men and the third leading cause of male cancer deaths. The best screening test to pick up prostate cancer in its early, more treatable, stages is a rectal examination. The American Cancer Society recommends that all men 40 and over have a rectal and prostate examination once a year.

After you've been treated for prostate cancer, your doctor will examine you periodically to check for any signs of recurrence. Depending on how much the cancer had spread initially, the exam will include a rectal examination, blood tests, X-rays and scans.

Q. I'm a healthy person who recently had a 12-hour "bug." The main symptoms were vomiting and diarrhea. My major concern was dehydration, but I also wondered what causes this problem, how dangerous it is for a healthy person, and what should one do?

A. It sounds like you had a stomach virus or intestinal flu -- what doctors call gastroenteritis, meaning inflammation of the stomach (gastro) and intestines (enteritis) due to a viral infection.

Three common causes of sudden vomiting and diarrhea are viral infections, bacterial infections and food poisoning, which is actually due to toxic substances released by bacteria that have grown in improperly prepared food.

In addition to vomiting and diarrhea, symptoms common to these conditions include stomach cramps, muscle aches and feeling generally ill. Viral infections and food poisoning usually run their course within 24 hours. Bacterial infections tend to last longer and be associated with more worrisome symptoms, like high fever, bloody diarrhea and more severe abdominal pain.

For healthy people, short episodes of vomiting and diarrhea, though bothersome, are generally not serious threats to health. The best thing you can do for this problem is keep up your fluid intake. Call your doctor for any of the worrisome signs I mentioned or if it's not getting better within 24 hours. It would be unusual for healthy adults to become severely dehydrated within 24 hours.

People often take medicines to check a bout of diarrhea, but doctors sometimes would rather not prescribe drugs for this purpose. The reasons are that anti-diarrhea medications can sometimes actually prolong the course of some bacterial intestinal infections and make them worse, and that most viral intestinal infections soon get better on their own.

Q. Every now and then I get a burning in my tongue. I notice that after I eat, the burning goes away. When I look in the mirror, I don't see any sores or anything unusual. I wear dentures. What could this be?

A. Your symptoms can be an early sign of inflammation of the tongue muscle or a problem with the nerves of the tongue.

Inflammation of the tongue is called glossitis, from glossa, the Greek word for tongue, and itis, meaning inflammation. Cigarette smoking and other irritating substances can cause glossitis. Because you wear dentures, and the burning seems to clear after eating, I wonder if your tongue is sensitive to your denture adhesive. Another explanation is that eating temporarily masks a low level of tongue irritation that you only notice when not distracted by something else.

Other causes of glossitis are vitamin deficiencies -- especially niacin, riboflavin, folic acid and vitamins B12 and C -- and iron deficiency.

Some women develop burning of the tongue around menopause, but it's uncertain whether this condition improves with estrogen hormone therapy.

Mouth infections and skin disorders affecting the tongue may also produce burning, but they would also make your tongue look different from usual.

Diabetes or drinking too much alcohol can lead to nerve damage that causes burning sensations.

Finally, various foods or medicines may set your tongue to burning. Common food offenders are milk, oranges, tomatoes, eggs, nuts and chocolate. Medications that occasionally cause glossitis include anticancer agents and certain antibiotics, antidepressants, and anti-inflammatory drugs.

Many people with tongue burning undergo careful investigation only to have nothing show up. If your doctor or dentist can't find anything wrong and your symptoms are very distressing, you might ask about being referred to the Taste and Smell Clinic, which specializes in disorders of taste and smell, including glossitis. The address is 5125 MacArthur Blvd. NW, Washington, D.C. 20007; 625-7559.