Khaled el-Masri is seeking ¿50,000 ($69,000) in compensation and an apology from Macedonia, following failed attempts to have his case heard in courts in the United States and Germany.
El-Masri, who is of Lebanese descent, says he was brutally interrogated at a secret CIA-run prison in Afghanistan for more than four months after being kidnapped from Macedonia in 2003, apparently mistaken for a terror suspect.
He said he went on hunger strike for 27 days and was eventually flown back to Europe and abandoned in a mountainous area in Albania.
Clara Gutteridge, an international activist against the United States' so-called extraordinary rendition program - abducting and interrogating terror suspects without court sanction - testified at the Skopje court on the first day of the proceedings.
But judge Sofija Milenkovska instructed her to limit her testimony to evidence and events that occurred in Macedonia - and not details of el-Masri's alleged flight itinerary to Afghanistan.
"It seems that the strategy of the Macedonian government in this case is not to address the evidence that have been presented to them, but simply continue to deny, deny and deny," Gutteridge told The Associated Press after the hearing. "The fact that they are not responding to the evidence ... just shows yet again that there are kind of structural and institutional reasons that make extremely difficult to get anywhere near the truth in this case."
Gutteridge studies rendition cases for the London-based group Reprieve, which campaigns against the death penalty and prison abuse.
Authorities in Macedonia deny any involvement in el-Masri's alleged kidnapping and are seeking to have the case dismissed.
U.S. officials have refused to comment publicly on the case, but diplomatic cables released by WikiLeaks website show that diplomats in Germany and Macedonia were at pains to keep the case out of the news and the courts.
In a cable from the U.S. Embassy in Skopje, Macedonia, dated Feb. 6, 2006, then-Prime Minister Vlado Buckovski is cited as promising the U.S. ambassador he would continue to refuse local press requests to discuss the el-Masri case.
In the United States, el-Masri filed a lawsuit against former CIA director George Tenet with the aid of the American Civil Liberties Union. But the complaint was never heard in a U.S. court on the grounds that it would reveal government secrets. That rejection was upheld by the U.S. Supreme Court in 2007.
In December, a German court rejected a lawsuit filed by el-Masri seeking to force Berlin into prosecuting suspected CIA agents who allegedly illegally detained him.
In Macedonia, el-Masri's lawyers say they are seeking compensation on the grounds that Macedonia sanctioned his alleged abduction and subsequently blocked any investigation into the incident.
They said the trial is likely to last at least two years.
El-Masri was not in court for Friday's hearing. He is currently serving a two-year prison sentence for assaulting the mayor of his home town in Germany.
ACLU presentation of el-Masri case: http://www.aclu.org/national-security/el-masri-v-tenet