QUESTION: I am a 72-year-old female. My health is good except for the usual aches and pains of aging. One of the things that bothered me was leg pain (in the calf, both legs). I had to stop my evening walks, which made me feel so good and sleep so well. The pains would come on about halfway through the walk - a half mile - and last about 10 minutes. After that, I would not have the pain. My doctor listens to me. He gave me pentoxifylline to take. Like magic it worked. I have not had the pain and have been back at my walks for three weeks. What is this medicine? - Mrs. L.T.

ANSWER: I've mentioned this relatively new medicine before, perhaps by its trade name, Trental. It is a good medicine and works by making blood cells more elastic, thus permitting their easier passage through the tiny arteries of our microcirculation. Its classic use is for claudication, the intermittent deficiency in local circulation to the calf muscles when walking.As impressive as Trental is, it will not work in every case, like yours. In fact, it is most helpful in milder claudication. Nor is it a substitute for vessel surgery, when that is needed. It can, however, help the patient improve his leg circulation on his own, by permitting longer walking distances and better circulation that way. I am sending on the leg pain report. Other readers may order by writing: Dr. Donohue/No.20, Box 830, Gibbstown, NJ 08027-9909, enclosing a long, stamped, self-addressed envelope and $2.

QUESTION: We were frightened recently when we noticed a reddish stain in our child's diaper. He is a month and a half and has been healthy. The pediatrician was not surprised at the stain but tested his urine and did a general checkup. He could not come up with anything. Can you comment? It seems to have gone away since then. - B.L.

ANSWER: Many benign occurrences can cause a reddish diaper stain. Chief among them is the simple presence of certain urinary crystals that alter color on exposure to air or on cooling. That is not serious.

In newborns, blood may indeed be found in the stool. It usually represents lingering traces of the baby's ingestion of maternal blood via the placenta. However, most often the answer is much simpler - food dyes with which the immature system does not cope well, red berries or minor anal, vaginal or post-circumcision abrasions. An intestinal infection can be present.

Parents are advised to report such occurrences. You did and had the more serious causes of diaper stain ruled out.

QUESTION: I read recently that we should not use bone-meal calcium supplement. What about calcium carbonate? Is it good to use? - Mrs. C.F.

ANSWER: Oyster-shell calcium is calcium carbonate. It is an acceptable form of calcium supplement. Bone-meal calcium has occasionally been found tainted with lead, prompting the caution.

Dr. Donohue welcomes reader mail but regrets that, due to the tremendous volume received daily, he is unable to answer individual letters. Readers' questions are incorporated in his column whenever possible.