About 5,000 people have taken part in a protest in Paris linking critics of a gay marriage bill to homophobia.
The rally came as an image apparently showing the victim of a homophobic attack went viral on social media.
Gay rights organisations say homosexuals are being increasingly targeted amid opposition to government plans to give gay couples in France the right to marry and adopt children.
Opponents of the bill have denied homophobia and denounced violence.
France's Socialist government is planning to change the law this year. Its proposals are currently being debated in the Senate.
Opinion polls suggest that around 55-60% of French people support gay marriage, but only about 50% approve of gay adoption.
The anti-gay marriage lobby, backed by the Catholic Church and right-wing opposition, has already held large marches in Paris.
It argues the move would undermine an essential building block of society.
Supporters of gay marriage took to the streets on Wednesday, waving placards reading "Homophobia kills" and "Our love is stronger than your hate".
Among them was Wilfred de Bruijn, a Paris librarian who says he and his partner were beaten up while walking arm in arm.
A photograph of his bruised and cut face has been shared widely on social networking sites.
"I certainly feel there's been an increase in homophobia,'' Mr de Bruijn told AP.
"What [the anti-gay marriage campaign] are saying is that they're not homophobic: lesbians and gays are nice people, but don't let them get close to children - that's very dangerous.
"It's OK for them to live together, but not like other couples with the same protection because it's not really the same thing.''
Frigide Barjot, an activist who has led protests against the bill, has insisted that the anti-gay marriage movement is opposed to violence.
Speaking on RMC radio, she said: "We don't want violence. We denounce this violence and these acts, we have nothing to do with fundamentalists or extremists."