Five Bulgarian nurses and a Palestinian doctor in Libya accused of making false claims of torture have pleaded not guilty to charges of slander.
First a death sentence, now a slander trial for the foreign medics
The six were sentenced to death in a separate trial last year for infecting hundreds of Libyan children with HIV.
They say they made false confessions, admitting to infecting the children, because investigators tortured them.
A Libyan police officer and a doctor claim nearly $4m (£2m) each in compensation in damages.
Both were acquitted of torture charges in 2005.
Tensions were high in the courtroom for the hearing in the slander trial, says the BBC's Rana Jawad in Tripoli.
"You should be ashamed of your crimes," said the Palestinian doctor Ashraf Ahmad Juma.
"You tortured us and now you are prosecuting us."
Police officer Juma al-Mishri said the lawsuit was not about money but rather about regaining their dignity.
He and doctor Abdulmajid al-Shoul want $3.9m (£1.98m) in compensation for damage to their reputation, and legal expenses.
Libya's chief prosecutor has asked for the maximum penalty for the medics - up to six years in prison.
The plaintiffs and eight other policemen were acquitted of torture in a criminal trial in 2005.
The 10 men investigated the role of the foreign medical workers in the HIV infections amongst hundreds of children in Benghazi.
The medics have been in detention since 1999, during which time 52 of the 426 infected children have died of Aids.
They have protested their innocence throughout.
International health experts have repeatedly said that the Benghazi HIV epidemic was caused by poor hygiene long before the foreign medics arrived.
The five Bulgarians and the Palestinian have appealed against their death sentences and are awaiting a Supreme Court hearing, which is expected in May.