Long before the little blue pill there was maca.

And Horny Goat Weed, catuaba and ashwagandha - plant aphrodisiacs that people in far-flung parts of the world have used for hundreds of years to improve their sex lives.

In tea, capsule and food form, these and other plant remedies may be poised to start a sexual revolution here, and Chris Kilham is taking up the charge.

Kilham, 52, is the explorer-in-residence - or, as he calls himself, medicine hunter - at the University of Massachusetts at Amherst, where he teaches ethnobotany.

He also is the author of the new book Hot Plants (St. Martin's Griffin, $12.95), which chronicles his global pursuit of proven sex boosters for men and women.

The intrepid explorer, who says he stumbled onto libido boosters while investigating medicinal plants used in foreign countries, also helped develop supplement formulas - Hot Plants for Her, Hot Plants for Him - based on his research.

"When I first heard of sexual enhancements from plants, I sort of assumed it wasn't real," he says. "But as I encountered more and more, I realized it was my attitude that wasn't real.

"You don't have something that people do for 2 or 3 thousand years, millions of people, if there wasn't justification for it," Kilham adds.

Au contraire, says the U.S. Food and Drug Administration, which holds that a long tradition of use doesn't equal scientific proof. It says sexual effects of aphrodisiacs are based in "folklore, not fact."

A middle ground is taken by Jennifer Berman, the director of the Female Sexual Medicine Center at UCLA.

"There are definitely herbal products that can enhance health, wellness and sexuality," Berman says. "The problem is they aren't regulated by the FDA and it's hard to know how much you need to take to see a beneficial effect. And just because they are herbs doesn't mean they are safe and they can interact with other medications as well."

Berman says there is no "magic herbal pill medication" that immediately improves sexual vitality, yet she sometimes prescribes herbal supplements as part of a patient's overall regimen, particularly for women who can't or don't want to take hormonal therapies.

Debate aside, Kilham is savvy enough to hear the cry for help coming from the bedrooms of America and thinks the "hot plants" can help.

According to the National Health and Social Life Survey, about 43 percent of women and 31 percent of men experience sexual dysfunction - numbers that are likely to grow as baby boomers see their hormones wane and energy flag in mid-life.

That trend is coinciding with another: Americans' growing acceptance and use of dietary supplements and herbal remedies.

The National Center for Complementary and Alternative Medicine, part of the National Institutes of Health, says 19 percent of adults use natural products such as herbs, botanicals and enzymes to treat and prevent disease.

Sexual health supplements rank near the bottom of the supplement market - just above insomnia remedies and below those aimed at mood health.

Still, they raked in an estimated $185 million in sales in 2003, says Patrick Rea, research director at the Nutrition Business Journal based in San Diego, Calif.

Rea says sex boosters are the fastest growing category of the supplement business - up 21 percent in 2003, and still rolling thanks in part to the prolific marketing of sexual performance drugs such as Viagra, Cialis and Levitra.

"There is always going to be a segment of the potential consumer population that isn't interested in taking pharmaceutical drugs," Rea says. "They are looking for natural remedies."

That is, something that will put a little humma-humma into their sex lives.

Kilham focuses on 10 hot plants (see box) he says can restore desire, function and response, though other herbalists have their own favorites.

He met with traditional herbalists and medical researchers in such countries as Malaysia, Africa, Russia and China.

Some of the plant substances he touts have been subjected to scientific scrutiny, but he says proof for most lies in their safe use by "millions" of people over centuries.

That view is echoed by Mark Blumenthal, executive director and founder of the American Botanical Council in Austin, Texas, an independent nonprofit organization that researches and provides education about herbs.

"The overall bottom line is there is a growing body of both scientific research on animal and human level that continue to support the traditional, historical and empirical data that shows some of the herbal formulas can be useful," Blumenthal says.

People didn't give muira puama, the bark of a South American tree, the common name "potency wood," he says, without good reason.

Still, Blumenthal would like to see more scientific research like that conducted at Yale University's School of Medicine. Researchers there showed Asian ginseng increases nitric oxide in cells and dilates the vascular system - which may be why the herb has long been known in Asia as helpful for "old man's disease" - impotence.

But herbal plant remedies can have side effects, too.

Yohimbe, which yields the active ingredient yohimbine hydrochloride and is used in such prescription drugs as Yocon for erectile dysfunction, can cause a rapid heartbeat, nervousness and insomnia in its herbal and pharmaceutical forms. People with conditions such as heart and liver disease, or on certain medications, shouldn't take it.

Kilham promotes yohimbe, but warns it is not appropriate for all people - in fact, he advises any readers of his book who have medical conditions to consult a doctor before trying hot plants.

Then, if you're game, put maca at the top of list. It's a hot plant all-star, according to Kilham.

A staple vegetable in Peru, he describes the root as "a food for epic sex." It can increase strength, energy, stamina, libido and sexual function.

"I make maca blender drinks in the morning and just feel totally super-charged. It's a great thing for stamina," he says.

He calls tongkat ali, a root native to Malaysia and several other southeast Asia countries, an "herbal Viagra." Kilham says it boosts testosterone, energy and muscle mass.

Another favorite: rhodiola rosea, a plant whose root gives off a rose-like smell, found in Siberia. It, too, is an energy and stamina booster and aphrodisiac that works especially well for women.

Kilham's top 10 plants can be used individually - and are available that way from numerous manufacturers. He collaborated with Enzymatic Therapy of Green Bay, Wisc., to come up with combination formulas tailored to men and women.

"By putting in a number of plants, there is a higher likelihood an individual will get results," he says of his blends.

Some local herbalists say Kilham's approach is far too simplistic. Minghau Zhang, a certified Chinese herbologist who was trained as a medical doctor in China, says figuring out why someone's sex life is unsatisfactory is "really complicated."

In China, there are thousands of herbal extracts that have been found helpful for libido and performance problems. At Ming's Oriental Health & Wellness Clinic, the backroom pharmacy is stocked with dozens of herbal tea extracts she mixes according to each client's individual needs.

Yin Yang Huo (Horny Goat Weed). Xian Mao. Tu Si Zi. Yang Qi Shi - whose Chinese name draws a laugh from Ming. "The name tells you 'It Goes Up.' "

"It takes a good practitioner, who makes the right diagnosis, makes the right formula and the right dose," she says.

Merry Lycett Harrison of Millcreek Herbs also prefers to take a holistic approach, addressing many factors that may affect libido, such as diet, stress and fatigue.

"I work to remedy those things rather than ramp up someone's libido," Harrison says. "I don't just throw herbs at people. Herbs have these niches and I can match the herb to the niche. It's the best of all worlds."

But are there herbs that help? Yes, she says. "What a lot of them do is help regulate vascular function in the reproductive organs."

Or promote vitality and relaxation.

Take damiana, for instance, which is available in tea form. "It can relax you," Harrison says. "You do feel really good physically. I can see how it would contribute to the moment if one came up.

"If you stay away from herbs that are harsh, you can find many that will enhance your sex life through other means than stimulating you too much," she says.

Kilham says proof the hot plants work comes from people who have tried them, though none of them are instant fixes.

"I have had reactions, from the mischievous grins of guys who have better erectile function than they have had in a long time, a 'Hey, I'm back' kind of thing. I have had a couple calls from women completely in tears who'd given up on having a sex life," he says.

The plants also can up the fireworks for those with healthy sex lives.

"For the most part, the people who are choosing to use the hot plants are more in the baby boom generation," Kilham says. "But there is a younger user group who are not having sexual problems and just like the idea they can take something to make it hotter, last longer and make it more thrilling."

And yes, Kilham practices what he preaches.