Republican Todd Akin acknowledged Friday that he was arrested in an anti-abortion protest about 25 years ago.
In Kansas City for a news conference, the U.S. Senate candidate didn't provide many details.
But in an Internet video about the incident, Akin is shown saying, "You know, don't tell anybody I'm a jailbird. A bunch of us sat in front of these doors and the police gave us a ride to the free hotel for a while, and you know how it goes."
On Friday, Akin, who is battling Democratic incumbent Claire McCaskill, characterized the incident as a "peaceful" protest.
"As I've made very clear, I don't apologize for being pro-life. I stand up for the things I believe in," he said.
Akin again defended remarks he made Thursday when he said McCaskill had not been very "ladylike" in their first Senate debate a week ago when she used an aggressive strategy toward Akin. He said the use of the word was not a big deal, pointing out that the wife of the president is known as the "first lady."
The terms "gentleman" and "lady" are "pretty self-explanatory terms," Akin said. "I was using them just as the English language uses those terms. It seems that some people want to take offense at words. It seems to me the offensive thing is a voting record that's destructive to the people of our state."
Akin insisted that "a whole lot of women" are backing his campaign because of the struggling economy and McCaskill's push to get the federal government "involved in everything."
In an appearance Friday on MSNBC's "Morning Joe" show, McCaskill said Akin was frustrated because he wasn't ready to debate her.
"I don't know exactly what his accusation that I'm not ladylike means," McCaskill said. "I think the debate was tough for Todd because I went through the list of his very, very extreme positions and I think he wasn't prepared to answer some of that."
McCaskill said Akin's latest comment was another in a long series of remarks that make him appear out of touch with mainstream America.
"This is somebody who kind of makes Michele Bachmann look like a hippie," she said, referring to the Minnesota congresswoman who ran for the GOP presidential nomination. "He is very much in a group of people that would never be part of a compromise that we need to find to address the fiscal cliff. Todd is going to be part of a kind of fringe caucus that wants to convince everyone that the government is the enemy. Government is not the answer, but it's not the enemy."
Also Friday, former senator Kit Bond of Missouri announced that he is backing Akin. Earlier, Bond was among several prominent Republicans calling on Akin to quit the race.
About 30 people, some with placards, showed up to protest at Akin's campaign stop.