According to the military, approximately 500 active-duty soldiers have refused vaccination orders. Just how many reservists have been spurred by dissatisfaction with the vaccination program to leave military service overall is difficult to know. The GAO survey is preliminary and the Pentagon doesn't specifically ask departing reservists whether anthrax vaccination contributed to their decisions.

At an Oct. 11 congressional hearing, Maj. Gen. Paul Weaver, the Air National Guard chief, acknowledged that pilots, on average, have left the guard earlier in the past two years than they did prior to the anthrax campaign, but said he had no data showing a definitive link. The reserves have fallen severely short of enrollment targets in the past two years, and the anthrax campaign has presumably played some role in this. Although he and other brass deny reports of massive resignations, Maj. Gen. Randall West, the Pentagon's point man on the anthrax program, admitted during the hearing that he was "very concerned" about the GAO report.

West and other officials say they had no choice but to deploy the anthrax vaccine after discovering that Iraq, North Korea and other nations have "weaponized" anthrax that could be used against American troops in battle or terrorist attacks.

"If the enemy uses it, and I haven't provided protection, I've got a lot of letters to write to a lot of mothers and fathers telling them why their sons and daughters died on the battlefield when I could have protected them," West said during the hearing.

That's the worst-case scenario. But many experienced airmen, who are typically in their late 30s and 40s, don't buy it.

"OK, I haven't looked at the intelligence reports, but you're telling me that an administrative clerk in Enid, Okla., needs to get an anthrax shot for force protection?" asks Marohn, of Plymouth, Ind.

"Was there anthrax in that bomb in Yemen?" rhetorically asks Savoie, the former Travis reservist.

Pilots, whose training typically can cost the military up to $6 million each, appear to be the group of reservists least willing to accept the anthrax vaccination. Most of those who have left are Air Force and Navy reservists, more than half of whom also fly commercial jets. Although the airlines are telling their pilots that the FDA has advised the FAA that the vaccine is safe, some, like Savoie and Hechtl, worry that an adverse reaction to the shot could ruin their civilian flying careers. Typically, these pilots may earn a $100,000 salary flying 10 hours a week for an airline, and less than $20,000 flying 10-15 hours a week for the reserves.

"We don't fly (in the reserves) for the money," says Savoie. "We do it for the fraternity. And because we're patriots." But in a peacetime military, the risk of vaccine side effects for a well-paid commercial pilot doesn't balance up well against the intangible benefit of service to one's country, particularly given the mistrust of the military that has been engendered by a series of congressional hearings on the issue.

"It's not so much the vaccine as the trust that's the issue here," says one pilot.

One adverse reaction that anthrax vaccinees have reported is vertigo -- "and that's a real career killer," says Hechtl.

"It's very hard to get your [pilot's] medical certificate, and these guys don't want to risk it," says Maj. Tom Rempfer, a former Connecticut Air Guard F-16 pilot who also flies for American Airlines out of Boston. Rempfer, 35, transferred to a nonflying reserve unit to avoid taking the shots.

Older pilots are both more aware of their rights than the average enlisted man, and more cynical about the military's history of dealing with medical problems, says a 40-year-old U.S. Navy pilot who flies P-3 observation planes over the Caribbean as part of the drug war.

"We know that the military is notorious for disavowing any knowledge of anything," says the reservist, who is also an American Airlines pilot but didn't want to be identified. "Their attitude is, 'We say this shot is completely safe, damn it, now take it.' And if you're a pilot, that scares you, because there does seem to be a problem out there. Are they going to replace your $100,000 salary if you grow a third arm or something? Or are they going to brand you as some kind of mental case and say, 'You're on your own.'? Because that's what they did with Agent Orange and the Gulf War Syndrome, which they haven't resolved yet."

The P-3 pilot said everyone in his command ended up taking the shots after the commander passed out 3-inch-thick binders with pro and con articles about the vaccine. "They were very open about the process and that made a difference," he says. "They didn't go around threatening people with courts-martial."