About 80 percent of people in developing countries still rely on traditional medicine--based largely on species of plants and animals--for their primary health care. In the United States, some 25 percent of prescriptions are filled with drugs whose active ingredients are extracted or derived from plants. Sales of these plant-based drugs in the U.S. amounted to some $4.5 billion in 1980 and an estimated $15.5 billion in 1990. Other drugs are derived from animals and microorganisms.

The following is a short list of some of the drugs whose active ingredients are extracted or derived from plants:

The possibilities for developing new drugs from forest resources should figure heavily in any calculation of the forests' true worth. All 119 plant-derived drugs used worldwide in 1991 came from fewer than 90 of the 250,000 plant species that have been identified. Each such plant is a unique chemical factory, says Norman R. Farnsworth of the University of Illinois at Chicago, "capable of synthesizing unlimited numbers of highly complex and unusual chemical substances whose structures could [otherwise] escape the imagination . . . forever." In other words, scientists may be able to synthesize these plant compounds in the laboratory, but dreaming them up, rather than plucking them from the forest and then replicating them, is quite another matter.

How much money is this effort worth? Since the mid-1960s, says Farnsworth, one-fourth of all prescription drugs dispensed from American pharmacies contained active ingredients derived from flowering plants. Commercially, these plant-derived medicines are worth about $14 billion a year in the United States and $40 billion worldwide. In 1985, Lilly Research Laboratories sold roughly $100 million worth of vincristine and vinblastine -- the periwinkle derivatives used to treat childhood leukemia and Hodgkin's disease -- and turned a stunning 8 percent profit.

Surprisingly, U.S. pharmaceutical companies do very little research on developing new drugs from wild plants. Why? For one thing, the industry has come to rely more on synthesized chemicals than on natural compounds for drugs, so the backlog of active natural substances still waiting to be tested is growing. For another, drug companies worry about whther they will be able to patent uses of natural products. On the other hand, in the early 1990s, the U.S. National Cancer Institute earmarked $8 million to screen 50,000 natural substances for activity against 100 cancer cell lines and the AIDS virus. China, Germany, India, and Japan, among others, are also screening wild species for new drugs.

Forest peoples originally discovered the medicinal uses of three-quarters of the plant-derived drugs currently in wide use. In the northwestern Amazon, indigenous people use at least 1,300 plant species to create drogas do certão or "wilderness drugs." In Southeast Asia, traditional hearlers use 6,500 different plants to treat malaria, stomach ulcers, syphilis, and other disorders. The World Health Organization estimates that 80 percent of people in the developing world rely on traditional medicines based largely on the use of medicinal plants.