Though veterinarians have long diagnosed behavioral problems in animals, the concept of canine PTSD is only about 18 months old, and still being debated. But it has gained vogue among military veterinarians, who have been seeing patterns of troubling behavior among dogs exposed to explosions, gunfire and other combat-related violence in Iraq and Afghanistan.

Like humans with the analogous disorder, different dogs show different symptoms. Some become hyper-vigilant. Others avoid buildings or work areas that they had previously been comfortable in. Some undergo sharp changes in temperament, becoming unusually aggressive with their handlers, or clingy and timid. Most crucially, many stop doing the tasks they were trained to perform.

“If the dog is trained to find improvised explosives and it looks like it’s working, but isn’t, it’s not just the dog that’s at risk,” Dr. Burghardt said. “This is a human health issue as well.”

That the military is taking a serious interest in canine PTSD underscores the importance of working dogs in the current wars. Once used primarily as furry sentries, military dogs — most are German shepherds, followed by Belgian Malinois and Labrador retrievers — have branched out into an array of specialized tasks.

They are widely considered the most effective tools for detecting the improvised explosive devices, or I.E.D.’s, frequently used in Afghanistan. Typically made from fertilizer and chemicals, and containing little or no metal, those buried bombs can be nearly impossible to find with standard mine-sweeping instruments. In the past three years, I.E.D.’s have become the major cause of casualties in Afghanistan.