The fruit of saw palmetto, known to botanists as Serenoa repens, has been used in Europe to relieve the symptoms of enlarged prostates for decades. Doctors there routinely prescribe it.

But in the United States, saw palmetto has been relegated to the ranks of dietary supplements, and until recently enjoying little sanction from medical doctors.

Even without official approval of the medical establishment, palmetto has become the fifth most popular medicinal herb, according to the National Institutes of Health.

Noting the herb's popularity and the results of some short-term studies on its effectiveness, some doctors, particularly urologists, are beginning to discuss it with patients who have enlarged prostates, said Dr. Stephen E. Straus, director of the institutes' National Center for Complementary and Alternative Medicine.

"They say, `Let's give it a try,' " Dr. Straus said of the doctors' advice. "I wouldn't say they prescribe it, but they are willing to arouse some patients to follow that approach and see how it works out."

Faced with that trend, the institutes have commissioned the first longer-term studies of saw palmetto's effectiveness and side effects.

About half of all men over 50 are afflicted with swollen prostates, a noncancerous ailment formally known as benign prostatic hyperplasia, the institutes say. The condition accounts for at least 1.7 million doctor visits a year in the United States, with estimated health care costs exceeding $4 billion annually.

No one knows for sure how saw palmetto works, if it does. A theory is that it may inhibit absorption of a form of testosterone linked to the swelling of the prostate. Those questions are likely to be settled in clinics and laboratories.

But as with many herbal supplements, the process of creating a saw palmetto product begins in a different world, one of swamps and rattlesnakes, itinerant pickers and casual roadside markets.

Immokalee, a town of 14,000 people on the edge of the Everglades, is the epicenter of the market, which operates about six weeks a year, from mid-August to the end of September. The area, about 30 miles southeast of Fort Myers, has an abundance of berries and workers to pick them.

Pickers spend the cooler morning hours gathering berries; by 3 p.m. their berry-stuffed pickup trucks and vans start arriving at New Market Road, where buyers gather.

Harvesters typically sell to the highest bidder at the moment, and prices change frequently. Early last month, Timoeteo Resa, who was picking berries in Immokalee, received 45 cents a pound. At that price, workers can easily take home more than $100 in cash a day.

For consumers, a month's supply of saw palmetto ranges from $4 to $20, according to ConsumerLab.com, an online independent testing laboratory. Prescription medications for the prostate ailment can cost $35 to $100 a month.

Picking the berries is hard, unpleasant and sometimes dangerous, said Art Lozano, a berry buyer. "I don't do it," he said. "I hope I never have to do it. You should see the snakes they bring me."

Rattlesnakes are common in the thickets. Humid heat, turning the palmetto patches into steam baths, is a more constant foe. Most of the time, workers pick along roadsides and in vacant lots in peace. But sometimes, landowners call local deputies to complain, and the workers are asked to leave. Occasionally, they are fined for trespassing.

Once bought, the sacks of berries are poured into wooden bins big enough to hold 1,200 pounds of the fruit. The bins are loaded onto semitrailers and hauled away to be dried for preservation.

Where the berries go from there varies. Some are simply ground, stuffed in gel capsules and sold. Some make two trips across the Atlantic before they are sold.

Supplements like saw palmetto are subject to more rigorous manufacturing practices in Europe than in the United States. The saw palmetto capsules used in the N.I.H. studies are supplied by an Italian company, Indena, which was chosen because its product is considered high quality. The company buys the dried saw palmetto berries from Immokalee and ships them to Italy, where their essence is extracted at high pressure with the help of carbon dioxide.

The extract is then sent to France, where the concentration is enhanced, returned to Italy and onward to Florida, where it is put into gel capsules in Tampa. From there it is sent to study participants. The extract is tested several times in the process to make sure it meets certain chemical standards, said Dr. Edward M. Croom Jr., the scientific and regulatory affairs manager for Indena USA East.

Dr. Straus of the health institutes said that the lack of standardization in manufacturing and labeling of supplements was a problem for consumers. The agency has tested the contents of a variety of herbal supplements and "the variability is enormous," he said.

"In some cases, people will buy a bottle of an herbal supplement like they would buy a bottle of wine — if it has a fancier label and costs more it's going to be better — and that's not necessarily a good assumption."

People may buy saw palmetto like wine, but the berries, which are orange when ripe, smell like the foulest home-brew imaginable as they sit in the sun at Immokalee's berry market.

The berries' resemblance to anything healthful or attractive fades even more when they are trucked a few miles out of town to Plantation Medicinals, one of the largest saw-palmetto processors in the area. Pungent and acrid do not begin to describe the odor emanating from the company's berry dryers.

Michael Huffman, the chairman of Plantation, has long been immune to the berries' aroma.

"Smells like money," Mr. Huffman said.