For 12 years, employees of the Howard County Circuit Court clerk's office had complained of headaches, respiratory problems and a general sense of the blahs. They'd feel fine on the weekends, they said, but come back to find that the place smelled like a locker room or rotten potatoes.

So in early August, fed up with years of breathing bad air, they threatened a sickout.

Enter Barney. Not the giant purple dinosaur. The 2-year-old mold-sniffing dog.

Margaret D. Rappaport, clerk of the Circuit Court, had long suspected mold as the culprit in their windowless ground-floor office at the tiny Ellicott City courthouse. Several times over the past 12 years, she has brought in county officials to try to fix the problem. Mold remains visible in several locations, including two courtrooms. She was mulling over the options when a colleague steered her to Barney's owners, David Marcelli and his wife, Rondra, of Westminster.

"We have the bomb dog and the drug dog, so why not the mold dog? It seemed like it might be an easy answer," said Sheri German, who met the Marcellis at the Howard County Fair. A five-year veteran of the clerk's office, she said she suffers from tearing eyes and an itchy throat while on the job.

A few days later, Barney, a mixed breed of indistinguishable ancestry who appears to be part Labrador retriever, was on the case in the clerk's office. Barney, David Marcelli said, has been trained to detect 18 types of mold as well as a bacteria commonly found in rotting wood.

It didn't take long. He sat several times while ambling on a leash through the clerk's office -- a sure sign he was finding mold, Marcelli said.

"If that was a bomb dog, I'd be getting the hell out of here," one sheriff's deputy said as he watched Barney sniff the rugs and bookcases and hit the deck repeatedly.

At one point, while in the document room, Barney moved low and rolled over several times on the carpet. "There was so much mold, he didn't know which way to go," Rappaport said.

Last week, Barney's detective work appeared to have paid off. In a three-page report by a laboratory in Portland, Ore., technicians appear to have found evidence of several kinds of gunk, some of it potentially toxic, in several parts of the clerk's office. Much of the mold, it appears, is in the ceiling tiles, probably caused by a leaking roof that the county is already scheduled to fix.

Howard County will also remove carpeting and put in a tile floor and take other steps to get rid of the mold, said James M. Irvin, Howard County's director of public works.

"There were some legitimate problems in there," he said. "We hope this latest effort will bring closure." He said the cost of the cleanup is not known.

Meanwhile, Rappaport is on to her next project: finding a way to clean out the mold that appears to be clinging to many of the 50,000 pieces of paper shelved in the document room. She is checking into an ozone generator, a machine that generates molecules that help wipe out mold.

In the meantime, she feels vindicated.

"That dog is worth his weight in gold," she said.

At one point in the clerk's office, Barney, pictured with owner and handler David Marcelli, rolled over several times. "There was so much mold, he didn't know which way to go," Margaret D. Rappaport said.