The refusals have raised the number of detainees who have stayed away from the proceedings to 14, a military official said on Sunday.
The first prisoner who declined to appear on Saturday was a 24-year-old who allegedly had been studying in the United States before travelling to his undisclosed home country and then to Afghanistan in June 2001, said Pentagon spokeswoman, Navy Commander Beci Brenton.
He is alleged to have manned a military observation post for the Taliban in Kabul, about two weeks after the 11 September attacks in the United States. The military also said he was linked to several individuals suspected of being involved with Usama bin Ladin's al-Qaida network.
The review tribunals have been set up to evaluate whether each of the 585 detainees at the prison are properly held as an "enemy combatant" or should be freed. They are separate from a military commission that held pre-trial hearings for four men this week.
The second prisoner who refused to appear is a 37-year-old who travelled to Afghanistan several weeks after September 11 to work for al-Wafa, a charity that Brenton said helped fund al-Qaida.
Of the 42 cases heard on Saturday, the military has decided against releasing 14 detainees so far. Findings on others have yet to be released.
The military is not releasing names of prisoners in the hearings, which it calls Combatant Status Review Tribunals.
Australia considers trial
An Australian official suggested they might follow the United States' lead and revive military commissions to try war crimes suspects.
In an interview published on Sunday, Australian Attorney General Philip Ruddock said: "We are at war with people who are not donning uniforms, who do not accept rules of engagement, who do not accept the Geneva Convention and who deliberately target civilians."
He added: "So what you are dealing with is something that is quite different to anything we've ever had to put up with ... that's why we've got to get our armour ready."
Human rights lawyers have branded the hearings as a sham, pointing out detainees are not allowed lawyers and saying the officers hearing cases cannot be considered impartial.