French judges in Paris have been questioning IMF chief Christine Lagarde over a controversial payout made to a tycoon when she was finance minister.
She is being asked to explain her handling of a dispute in 2007 which resulted in some 400m euros (£342m; $516m) being paid to Bernard Tapie.
She appeared before the Court of Justice of the Republic (CJR), which investigates ministerial misconduct.
The IMF chief insists the award was the best solution at the time.
She could be placed under formal investigation for the decision to use arbitration, against advice from senior advisers, to settle a long-running court battle between the state and Mr Tapie, a supporter of the then French President, Nicolas Sarkozy.