"The prevailing attitude is: 'It's all in your head and you should go get your head on straight,"' Gerdes said.

But he believes there is a connection. He has seen the same symptoms over and over in patients who have no psychological bent toward hypochondria and nothing to gain from imagined illnesses.

He contrasts chemical exposure in oil fields with occupational asthma. Asthma caused by chemical exposure can be measured by decreased lung function and is recognized as a true malady. But no measurement exists for vertigo, muscle aches, blacking out and headaches.

"It would make sense for the governors in oil and gas states to get together and get their health departments together to take a look at this. The health departments could do a coordinated study and share experiences and knowledge," said Lance Astrella, a Denver attorney who once worked for the oil and gas industry but now represents those across the country who have been wronged by the industry.

He doesn't have cases pending in the Piceance Basin, and says cases such as Hoffmeister's are nearly impossible to prove in court.

The anecdotal litany of complaints grows with the number of wells drilled. But state and federal agencies largely have taken a hands-off approach.

The Environmental Protection Agency doesn't regulate individual oil and gas-well emissions because, unlike power plants and factories, wells are considered small sources of pollution.

The Colorado Department of Public Health and Environment has oversight of emissions but has no comprehensive method for sampling air around individual wells. The chemicals evaporating off ponds of chemical-laden production water aren't measured. And there is no standard for the diesel exhaust from idling trucks and rig motors.

Sorting out the noxious chemicals that might be in the air from all sources — be it a rig or a neighbor's fireplace — would be nearly impossible, said Mike Silverstein, deputy director of the health department's air-quality-control division.

When residents near oil fields complain about problems that often originate with wells on neighboring properties, they have called Silverstein as well as law enforcement, senators, energy companies and local officials — often without satisfactory results.

The state agency officially charged with overseeing such complaints — the Colorado Oil and Gas Conservation Commission — must respond to calls, but the commission has no health experts on staff.

Tricia Beaver, a spokeswoman for the commission, said the commission is doing what it is mandated to do in investigating complaints and has been consulting more with health officials in the past year.