SOMEWHERE IN THE jungle, says Paul Cox, the cure for AIDS or Alzheimer's might be growing on a tree. That's why this past week he's been in Rotuma, a remote island 600 miles north of Figi.

Cox, a professor at Brigham Young University, is one of the world's few ethnobiologists. Like a growing number of scientists, he believes nature may hold the cure for man's most troubling diseases. What makes Cox and other ethnobiologists unique is their insistence that the "old wives" and "witch doctors" of remote cultures can provide a shortcut to those cures.There are 250,000 species of plants in the world. Western medicine has made medicines out of only about 40 of them, he points out. That leaves a daunting 249,960 species still to explore.

Villagers in the rain forests of the South Pacific and the Amazon have been using these plants for thousands of years, Cox reasons. "They've already screened out what helps people and what doesn't work."

The rapid demise of both the rain forests and the cultures living in them means that finding medicinal plants is now "a race against time," he says.

"These are almost always oral traditions. So unless they're studied now, they're gone." Already it's hard to find villages where the natives don't offer him an aspirin.

Cox has been scouring the rain forests of the South Pacific for six years, interviewing local healers, then bringing back samples of the plants that have proved most useful. He turns those samples over to American chemists, who run lab tests to gauge their effectiveness against diseases like cancer and AIDS.

Cox stresses that he is not an herbalist. He wants the plants he unearths to be scientifically tested, with known constituents and side effects. "If I could be convinced that old tires had medicinal benefits, I'd be right out there looking at them," he says.

For the past two weeks Cox has been in Rotuma, a remote island not yet studied by botanists. Armed with a machete and plenty of mosquito repellent, plus a computer and a video camera, Cox hopes to learn about plants and cures that are brand new to Western eyes.

He is traveling with one of his graduate students, Will McClatchie, a pharmacist at the K-Mart in Orem. McClatchie generally spends his days surrounded by plastic bottles full of sinus tablets and pain killers but, like Cox, believes that scientists need to look to plants for better medicines.

Six years ago, when Cox first began his research effort in Samoa, U.S. drug companies "wouldn't even let me in the door," he says. Now, however, most major drug companies have begun to take a closer look at plants. The National Cancer Institute has tested more than 300 of the samples Cox has brought back from South Pacific jungles.

Three years ago, Cox helped save a Samoan rain forest literally as bulldozers were chugging toward it. The villagers of Falaelupo, on the island of Savaii in Western Samoa, had reluctantly agreed to sell part of their sacred rain forest so they could pay for a new school.

Cox happened to be there the day the bulldozers arrived and he quickly made the village elders an offer: He would find a way to raise money for the school if they would agree to keep the rain forest as a preserve.

"From that Samoan forest we've come up with three new compounds, one that shows anti-viral activity, and two that show anti-inflammatory activity."

If those or any other plants ever do become the basis for a new drug, Cox says he will make sure the villagers share in the royalties. "The people aren't my informants," he explains. "They're my colleagues." - Elaine Jarvik