French prosecutors have opened a murder inquiry into the death of Palestinian leader Yasser Arafat in 2004.
His family launched a case last month over claims that he was poisoned with polonium-210, a radioactive element.
Swiss scientists hired by a documentary crew say they found traces of polonium on some of Arafat's belongings.
The medical records of Arafat, who died at a military hospital near Paris in 2004, said he had a stroke resulting from a blood disorder.
However, many Palestinians continue to believe that Israel poisoned him. Israel has denied any involvement.
Others allege that he had Aids.
'Significant' polonium traces
Tuesday's decision by the court in the western Paris suburb of Nanterre followed the deposition of a civil suit in late July by Arafat's widow, Suha. The case does not name an alleged killer, but is brought against an unnamed perpetrator X.
French officials on Tuesday said prosecutors had agreed to begin a murder inquiry, but they have yet to appoint an investigating judge.
The BBC's Hugh Schofield in Paris says the French legal system is obliged to take the matter very seriously because of its diplomatic aspect, but the medical profession is generally sceptical about claims of radioactive poisoning.
A statement by Mrs Arafat's lawyers in Paris welcomed the decision by the court and said they would make no further comment to allow investigators to be able to pursue their inquiry with respect for secret information and without undue interference.
The Palestinian Authority also welcomed the move.
Senior official Saeb Erekat said President Mahmoud Abbas had officially requested the help of French President Francois Hollande in the investigation.
"We hope there will be a serious investigation to reveal the whole truth, in addition to an international investigation to identify all the parties involved in Arafat's martyrdom," he told the AFP news agency.
The inquiry stems from an al-Jazeera TV documentary broadcast early in July, which commissioned Lausanne University's Institute of Radiation Physics (IRA) to analyse Arafat's belongings, which his widow had kept.
The scientists told the channel that they had found "significant" traces of polonium-210 present in items including Arafat's trademark keffiyeh.
Mrs Arafat's lawyers have said she wants a French investigation to work alongside international inquiries being conducted by the Lausanne scientists.
Last week, the Swiss institute said it had received permission from Mrs Arafat and the Palestinian Authority to travel to Ramallah to analyse her late husband's remains for traces of polonium.
The Palestinian Authority said last month that it was willing to order the exhumation of Arafat's body from the stone-clad mausoleum in which it is buried in the presidential compound in Ramallah.
Arafat led the Palestine Liberation Organisation for 35 years and became the first president of the Palestinian Authority in 1996.
He fell violently ill in October 2004 and died two weeks later, at the age of 75, in a French military hospital.
French doctors bound by privacy rules did not release information about Arafat's condition.
In 2005, the New York Times obtained a copy of Arafat's medical records, which it said showed he died of a massive haemorrhagic stroke that resulted from a bleeding disorder caused by an unknown infection.
Experts who reviewed the records told the paper that it was highly unlikely that he had died of Aids or had been poisoned.