One newsletter defines it as `a subspecialty for new or presumed extinct species of all sizes.' Simply stated, cryptozoology is the study of animals that have not been recognized by Western science.

In 1982, a professor at a Vietnamese university was exploring the slopes of Mom Ray Mountain near the Cambodian border when he stumbled upon a strange footprint. Measuring 10-by-6 inches, it was wider than any human foot and had longer toes. Some speculated that the footprint might belong to a legendary creature called Nguoi Rung, or "Wildman."

To this day, no one knows for certain who -- or what -- made the footprint. Is "Wildman" an ape? Or more tantalizingly, could it be a human ancestor still hiding in Asian forests?

Though Nguoi Rung sounds like something from a Michael Crichton novel, new species are being discovered in Vietnam with startling regularity. During the last several years, scientists have identified five new mammals, including a barking deer, a pheasantlike bird and what one naturalist described as a "kind of goat, but a little bit strange." Not since the 19th century have so many mammals been discovered in such a short period of time.

The search for new creatures, or creatures believed to be extinct, has attracted serious investigators despite its quixotic nature. In fact, the field has a name -- cryptozoology -- coined by Belgian zoologist Bernard Heuvelmans from the Greek word kryptos, meaning hidden, unknown, secret. There even is an International Society of Cryptozoology with 900 members, a number of distinguished zoologists, naturalists and oceanographers among them.

Others came to the field by way of science fiction. Loren Coleman, a Maine researcher who has written extensively on cryptozoology, says that he was inspired by a science-fiction movie called Half-Human, about the yeti, or abominable snowman. "It showed me a reality that I hadn't heard about from my biology and natural-history teachers," he tells Insight. After earning undergraduate degrees in anthropology and zoology, he went on to get a graduate degree in psychology "so I'd know when people were lying to me."

An ability to ferret out the truth clearly is a crucial skill for a cryptozoologist. Coleman estimates that 20 percent of the reports he investigates prove to be genuine; the others tend to be cases of mistaken identity or outright hoaxes. Unquestionably, some reputed creatures seem to belong to the realm of pure fantasy, such as the chupacabra of Mexico, feared for its nasty habit of sucking the blood out of goats, and the New Jersey devil, a creature "three-and-a-half feet high, with a head like a collie and a face like a horse," which hasn't been seen since 1951.

But of all the undiscovered creatures that have fascinated cryptozoologists and the public, few have received as much attention as bigfoot (or Sasquatch) and the Loch Ness monster. In Portland, Ore., fans of the hirsute humanoid have formed the Western Bigfoot Society, with members from as far away as Sri Lanka. This summer the society will sponsor a mock trial in Carson, Wash., where the "defendant" will stand accused of killing a bigfoot, a crime that is actually on the books in Skamania County. The issue to be decided: Is bigfoot animal or human? "I get a lot of weirdos with stories about bigfoot coming out of flying saucers," admits Roy Crowe, the society's director. "On the other hand, I also get veterinarians and doctors. I never try to discourage anyone from attending our meetings."

Although there have been numerous reported sightings (on the East Coast and in the Midwest as well as in the Northwest), Crowe acknowledges that the existence of bigfoot is far from proved. The most convincing evidence he can recall is some 16mm footage taken of a mysterious creature in 1968. Experts still are debating its significance. Otherwise, Crowe says, "No matter how many tracks you find, they can always be faked. …