Four activists with the Ukrainian feminist organization Femen held a topless protest on St. Peter's Square to protest the Catholic Church's stand against same-sex marriage.
The four women were whisked away by police.
The protest occurred as Pope Benedict XVI was delivering a prayer from his studio overlooking the square.
The prayer was not interrupted.
Femen leader Inna Shevchenko, who was one of the protesters, told journalists, "Today we are here to protest against homophobia."
The demonstration coincided with a massive demonstration in the French capital, Paris, against French President Francois Hollande's plan to legalize gay marriage and allow gay couples to adopt children.
The campaign against Hollande's plan has been spearheaded by Catholic clergy in France.
Based on reporting by AP and dpa