French experts are examining what it is claimed are traces of chemical weapons used in Syria.
The samples were passed on to the French intelligence services by a team from Le Monde newspaper.
They say medical workers have described symptoms consistent with the use of sarin gas.
Under cover in and around Damascus for two months alongside Syrian rebels, the reporter and photographer also say they witnessed chemical attacks themselves.
The results are due in the next few days.
The US, French and Russian foreign ministers have said proof of the use of chemical weapons would be a game-changer.
The Syrian government and opposition have accused each other of using the weapons.
UN investigators have been held up by diplomatic wrangling and safety concerns.