Abuses at Abu Ghraib emerged after photographs were made public
Four Iraqi men say they are suing US military contractors for torturing them while they were detained at the Abu Ghraib prison near Baghdad.
The men, who were all released without charge, have brought separate lawsuits in four US courts.
One of the men said he was beaten, threatened with dogs and given electric shocks during four years at the prison.
CACI International, one of two companies named in the lawsuits, dismissed the claims as "baseless".
Three civilians, all said to be former employees of the two contractors, CACI and L-3 Communications Corp, have also been named in the cases.
Adel Nakhla of Maryland, Timothy Dugan of Ohio and Daniel Johnson of Seattle are accused of taking part in abuses during interrogations.
CACI said the claims were "unfounded and unsubstantiated", and the new lawsuits repeated "baseless allegations" from a previous lawsuit several years ago.
"These generic allegations of abuse, coupled with imaginary claims of conspiracy, remain unconnected to any CACI personnel," the company said in a statement.
Mr Johnson's lawyer also said the claims were false, and told the Associated Press his client had served his country "honourably" while working in Iraq.
'Hung from a pole'
The four plaintiffs were held in Abu Ghraib prison in 2003 and 2004.
Abuses at the prison were brought to light when photographs emerged of US soldiers mistreating prisoners in 2003.
One of the four plaintiffs, Waseem al-Quraishi, said he was electrocuted, beaten and hung from a pole for seven days.
Another, Mohammed Abdwaihed Towfek al-Taee, says he was forced to drink litres of water while his penis was tied to prevent him from urinating.
Military personnel have already been tried on criminal charges and imprisoned for abuses at Abu Ghraib, but no civilians have.
Tens of thousands of US civilians have worked on contract for the US military in Iraq, many of them in very sensitive roles such as in intelligence gathering and in combat.
The BBC's Adam Brookes in Washington says the question of whose laws they should obey, and who should hold them accountable when they do things wrong, remains one of the most vexed questions of the war.