A court in Milan has begun a hearing to decide whether to indict 25 alleged CIA agents and several Italians accused of kidnapping a Muslim cleric in 2003.
The cleric was allegedly flown out of Italy from a US military base
Osama Mustafa Hassan, or Abu Omar, was abducted from the streets of Milan and says he was then tortured in Egypt.
The case was an example of the US policy of rendition - transferring terror suspects abroad for questioning.
If the court decides to proceed with a trial it would be the first linked to the controversial practice.
Prosecutors say the cleric, who was suspected of links to terrorism, was plucked from a Milan street, driven to the Aviano military base and flown, via Germany, to his native Egypt, where he was secretly interrogated for six months.
Prosecutors allege the Italian secret service co-operated with the CIA in promoting and organising his abduction.
Twenty-six Americans have been named in the case - 25 of them alleged CIA agents and one air force officer at Aviano base. Six Italian secret service officials could also face kidnapping charges.
None of the accused Americans is thought to be still in Italy, and correspondents say it is unlikely the US would extradite them for trial.
Among those facing prosecution is the retired CIA station chief in Milan, Robert Seldon Lady, who was reportedly rushed back to America, leaving behind the villa he had bought with his life savings.
According to testimony compiled for the case, Mr Lady opposed the abduction but was later overruled by his boss in Rome, who is also a co-defendant.
Lead investigator Armando Spataro has appealed to the government of Prime Minister Romano Prodi to seek the extradition of the US suspects.
It has not indicated whether it will. The previous administration of Silvio Berlusconi rejected the request.
Among the Italians accused of kidnapping is the former head of Italy's military intelligence agency, Nicolo Pollari. Mr Pollari recently lost his job following a parliamentary inquiry.
None of the defendants was present for the hearing, which is expected to last for several days.
Abu Omar, who had been granted asylum in Italy, is still in custody in Egypt.