Two US tourists have had hydrochloric acid thrown in their faces at Marseille train station, French media say.
The victims, both in their early 20s, received treatment in hospital, but were released later in Sunday.
Two other members of their group were also attacked at Saint-Charles station, but did not get acid in their faces.
The incident is not believed to be terror-related. The attacker, described by police as a mentally unstable 41-year-old woman, has been arrested.
The report says she remained at the site after the attack, and showed photographs of herself with burns.
The group are Boston College students who are on a year in Europe, the college said in a statement.
"It appears that the students are fine, considering the circumstances, though they may require additional treatment for burns," it said.
Acid attacks around the world:
- In Britain the problem has become so acute there have been calls for parliament to act. One such attack was caught on camera in London last month
- In Berlin at the beginning of this year there was a series of acid attacks on women
- A former Miss Italy finalist has also been attacked
- Acid attacks have also been reported in the US, most recently in Arizona
- In South Asia acid attacks have been commonplace for many years - with one case on Wednesday involving two men in India who allegedly gang-raped a woman and then later attacked her with acid