The four, Corporal Charles Graner, Specialist Megan Ambuhl, Staff Sergeant Ivan Frederick and Specialist Javal Davis, are accused of among other charges, assault, coercion and conspiracy to mistreat inmates. They will appear on Monday.
The humiliation of the prisoners, seen in photographs taken by some of the suspects and made public by the media in April, caused outrage and has undermined the reputation of the United States, above all in Muslim countries.
During the two-day hearing - known as an Article 39 - a military judge could hear witnesses, take evidence and deal with procedural matters relating to the four, but nothing that touches on their guilt or innocence.
The hearing was originally due to take place in Baghdad on 21 June, but was moved to Mannheim, southern Germany amid security fears.
"This is a one-time only arrangement - all future proceedings will be held in Baghdad unless the military judge grants a venue change at a later date," the US military in Mannheim said in a statement.
Journalists were frisked before
entering the court room
Since Saddam Hussein's removal, people accused of "anti-coalition activities" have been detained at Abu Ghraib for months at a time, often without charge and usually having their cases reviewed only every six months.
The torture scandal has seen blame pushed from a group of guards up through the military echelons. It has embarrassed US Defence Secretary Donald Rumsfeld, but has not resulted in any sackings or resignations of high-ranking officials.
The hearing in Germany follows a court procedure in the US to determine whether Private Lyndie England, who was pictured holding a leash around the neck of a naked detainee, should face a court martial.
Rumsfeld has been embarrassed
by the scandal
That hearing has been halted so more witnesses can be called.
Attention in Mannheim will focus on Graner, who was photographed smiling, arms folded behind a hill of naked prisoners and whom England says is the father of her unborn child.
Witnesses in the hearing of England, who could face up to 38 years in jail, said the abuses at the prison usually started in the evening when Graner was in charge of the cell block.
England's lawyer has said she has been made a scapegoat for the army and that senior officers at the jail encouraged rough treatment and abuse to "soften up" detainees; a defence likely to be employed by the accused in Mannheim.