Australia has admitted it vaccinated its Iraq-bound troops against anthrax without disclosing the side-effects on soldiers sent to Afghanistan.
The US-led coalition claimed Iraq had biological weapons
The government has confirmed that most of the 1,500 troops deployed to fight the Taleban in 2001 become ill.
But officials have defended the decision not to tell soldiers heading for Iraq in 2003, saying they did not want to cause anxiety.
They also say they thought such problems were unlikely to be repeated.
The side-effects suffered by three in four of the troops sent to Afghanistan were revealed when confidential defence documents were released to The Australian newspaper under freedom-of-information rules.
The soldiers experienced symptoms including swelling, severe pain and 'flu-like illness after receiving their jabs.
The vaccination programme was suspended for several weeks, but resumed after an investigation, although the cause of the side-effects was never discovered.
Senior military doctors have said other factors - such as the temperature in Afghanistan and high physical workloads - could have contributed.
The defence minister had the jabs himself
In 2003, troops set to join the invasion of Iraq were not told of the problems.
At the time, Defence Minister Robert Hill insisted qualms about the shots - which were compulsory - were unfounded, and was vaccinated himself to demonstrate his confidence.
Nevertheless, some Australian servicemen and women were unconvinced. About 40 were sent home from the Gulf for refusing the jabs, though they have not faced disciplinary procedures.
However, no unusual rates of adverse reactions were reported from the Gulf.
On Saturday, the director general of the Defence Health Service defended the decision not to inform the troops deployed to Iraq of the side-effects.
"We were in a position where all we would have been able to tell them was that there had been a problem," Air Commodore Tony Austin told reporters.
"We had not been able to identify a cause from that and we had absolutely no evidence to suggest that we were likely to see that again, based on overseas experience and our own
experience when we reinstituted the programme in Iraq," he said.
"So, I think to have advised people of that would have been quite counterproductive. I think that would have increased anxiety levels amongst our people."
But the opposition defence spokesman Chris Evans demanded a public explanation from Mr Hill.
"The defence department hasn't been honest with the troops, hasn't been honest with the parliament, and the minister needs to provide answers as to what's gone on here," he said.