Libya accused the five nurses and the doctor, who has been granted Bulgarian citizenship last month, of deliberately infecting more than 400 Libyan children with HIV, the virus that can cause Aids.
February 1999- 19 Bulgarian medical workers are detained in an investigation into how children in a hospital in Benghazi became infected with HIV. Later, 13 are freed.
2000 - Trial begins. The medics say their confessions were extracted through torture.
September 2003 - French Aids expert, testifies the epidemic broke out the year before the Bulgarians arrived.
May 2004 - The nine Libyans and the Bulgarian doctor are acquitted, but the Palestinian doctor and the five Bulgarian nurses are found guilty and sentenced to death.
December 2005 - Supreme court overturns the death sentences, sending case back to a lower court for retrial.
December 2006 - After 7 month retrial, the six medics are again found guilty and sentenced to death.
July 22 - An EU team, including the wife of the French president, travel to Libya to press for the release of the health workers.
July 24, - The six arrive in Bulgaria and are granted a pardon by Bulgaria's president.
The six, jailed since 1999, deny infecting the children and say their confessions were extracted under duress.
They were sentenced to death by a Libyan court, a sentence that was later commuted to life in prison.
After a deal was reached with Libya on compensation and medical ties, the six were allowed to serve out their sentence in Bulgaria.
The group arrived in Bulgaria on board a plane with Cecilia Sarkozy, the French first lady, and Benita Ferrero-Waldner, the EU's commissioner for foreign affairs.
"I share the joy of their families and friends and of the government and people of Bulgaria. For over eight years, we have never forgotten the suffering of the medical staff who have shown such dignity and fortitude during their long ordeal," Ferrero-Waldner said.
Sergei Stanishev, the Bulgarian prime minister, said at the airport: "The return of the medics is a direct result of Bulgaria's membership in the European Union, of the solidarity which the EU showed Bulgaria."
Nicolas Sarkozy, the French president, said in a press conference on Tuesday that neither France nor the EU had made any payment to Libya.
"I can quite simply confirm to you that neither Europe nor France have made the slightest financial contribution to Libya," he told reporters in Paris.
But he thanked the Qatari government for its role in mediating an end to the crisis, and suggested it may have provided some form of additional assistance.
"I have had the opportunity to thank the Qatari authorities very warmly for their mediation and their humanitarian intervention. It's up to them to say if they have something to say on the subject," he said.