QUESTION: Thanks for your endeavors to enlighten us readers with your health column. My question: What are the "free radicals" you hear about, which are supposed to play a role in disease? - R.K.

ANSWER: Free radicals are undesired substances the body generates in the course of the millions of chemical processes that go on daily throughout life. Because they are undesirable, the body has ways of getting rid of free radicals under normal circumstances. I said under normal circumstances. If conditions arise where too many are formed or the disposal process is disrupted, these compounds hang around to damage cells. That's the basis of disease.A lot of research has gone into the nature and behavior of free radicals. Some authorities suggest that the accumulation of these compounds cause cells (and us) to age. And some theorize that free radicals lie at the heart of cancer development. It's interesting to note that free radicals are the agents that turn butter rancid.

The whole idea of free-radical effects has given rise to a new health industry promoting substances that defend against free radicals. Among them are enzymes, like superoxide dismutase. Vitamin A and E and selenium-containing compounds also buffer free radicals. But I must say that the appealing claims for such substances as a hedge against aging remain scientifically unproven as yet.

QUESTION: Regarding cluster headaches - unless you have suffered from them you cannot comprehend the unbearable pain. Three years ago, I learned to abort a full-blown cluster headache with high-flow oxygen. I don't understand why this treatment is not mentioned more often. If it can help one person the way it helped me, it's worth the effort. For me it's been a lifesaver. - L.L.N.

ANSWER: Oxygen can afford blessed relief for one with a cluster headache.

I have mentioned this from time to time but perhaps neglected to do so in the most recent discussion. It is, in fact, a bit difficult to carry around a ready supply tank of oxygen. One never knows when a headache will occur. Also, the patient has to have careful instruction on safety precautions and the precise limits of oxygen flow allowed. Too much pure oxygen can damage lungs. I'm glad you have been able to make good use of the therapy. The other aspects of cluster-headache treatment are discussed in the headaches report. Readers may order by writing: Dr. Donohue/No.15, Box 830, Gibbstown, NJ 08027-9909, enclosing a long, stamped (52 cents), self-addressed envelope and $2.

QUESTION: I have a frightening family background. My dad and both his brothers died early of heart attacks. I lead as healthy a life as I know how to, but I am always looking for new tips on what to do to counter this family history. Please comment. - Mrs. O.P.M.

ANSWER: You're approach is wise. One of every two deaths is heart-related, and even with your family history, you can mitigate the hand dealt you.

If you haven't had your cholesterol checked, do so. If it's high, and if a low-fat, low-cholesterol diet doesn't help, you might require drugs (unavailable before your dad died) to lower cholesterol. You can't even think about smoking, and you have to keep blood pressure within limits. You have to exercise and pay attention to your weight. You have to stay on the lean side. These few simple measures will more than counter the genetic factors working against your longevity.