A French senator has been questioned on suspicion of plying an MP with a drug without her knowing.
Joël Guerriau was detained at his home after the MP, identified as Sandrine Josso, allegedly had a drink with him and then complained of feeling unwell.
She was taken to hospital where samples are said to have revealed traces of the drug ecstasy in her system.
As a result of the tests she then filed a criminal complaint.
On Friday, police in Paris questioned the 66-year-old senator on suspicion of "administering to a person without their knowledge, a substance likely to diminish their judgement or self-control, to commit a rape or sexual assault".
Mr Guerriau is one of 18 independents in the French upper house and a member of the centrist Horizons party.
While he was in custody he was also challenged by Ms Josso who gave her account of what happened, French reports said. Her lawyer said the MP was still in a state of shock.
Julia Minkowski told AFP news agency the two politicians had known each other for about 10 years and spoke of the MP's "feeling of betrayal and total incomprehension".
The senator's lawyer, Rémi-Pierre Drai, gave an initial statement stressing that "we are miles away from the obscene interpretation that one might infer from reading initial reports in the press".
On Friday he said his client had been able to confirm forcefully his version of events, which did not acknowledge that any type of offence had been committed.
Mr Guerriau, 66, is a former banker who was elected to the Senate in 2011 and is vice-president of its foreign and military affairs committee. He became a local mayor in his 30s in the Loire-Atlantique area of western France.
Under laws that apply to someone described as caught in the act, prosecutors said that the senator was not eligible for parliamentary immunity.
Christophe Béchu, who is both a party colleague and minister of ecological transition, said Horizons officials would meet on Saturday to discuss his position. "He clearly won't be able to stay in the party if there is the slightest doubt surrounding the veracity of all this," he told French radio.