National Park Service spokesman Bob Miller said one little brown bat taken from hibernation at White Oaks Blowhole Cave tested positive for white-nose syndrome.
A news release from the Great Smoky Mountains National Park said the debilitating fungus was confirmed by the U.S. Geological Survey's National Wildlife Health Center in Madison, Wis.
Besides the one confirmed case, photos of Indiana brown bats in the cave show conditions consistent with early stages of the syndrome.
Park officials had taken precautions, hoping to protect bats from the malady.
"We closed all of the park's 17 caves and two mine complexes to any public entry a year ago to prevent the possible importation of the WNS pathogen on visitor's clothing or gear, but scientists have confirmed that bat-to-bat transmission of the fungus occurs," said Bill Stiver, a wildlife biologist at the park.
"We take this very seriously because national parks are often the primary refuge that endangered species can count on for protection," Stiver said.
White Oak Blowhole Cave has the largest known hibernating colony of Indiana bats in Tennessee.
The syndrome is called white-nose because a white fungus forms on the faces of infected animals. Biologists are investigating how it affects the bats.
The news release said it's possible that bats become restless during hibernation, moving about the cave and burning up fat reserves or losing body water they need to survive the winter.
Stiver said bats may be hugely important in controlling insects, but many might misunderstand and even dislike them.
"We are very concerned about the potential decline of bats from both an ecological and human health standpoint," he said.