Speaking to Politico, McCain said he did not know how many residences he and his wealthy wife Cindy own, adding, "I'll have my staff get to you" with the information.
Obama has been taking a beating from the McCain campaign, which labels him an "elitist."
But Thursday the Democrat got a measure of revenge, Fox News reported, telling a town hall audience outside Richmond, Va.: "Somebody asked John McCain, 'How many houses do you have?' and he said, 'I'm not sure -- I'll have to check with my staff.' True quote! 'I'm not sure, I'll have to check with my staff.' So they asked his staff and he said, 'At least four.' 'At least four.'"
The McCain camp was equally waspish in reply.
"We're delighted to have a real estate debate with Barack Obama," said spokesman Brian Rogers, The Washington Post reported. "(Obama's Chicago house is) a frickin' mansion. He doesn't tell people that. You have a mansion you bought in a shady deal with a convicted felon."
The reference was to Tony Rezko, a former friend and financial backer convicted of fraud and bribery charges this year. Obama bought a strip of land from neighbor Rezko for more than the assessed price, which made Obama's land more valuable.
"That's fair game now," Rogers said. "You are going to see more of that now that this issue has been joined. You'll see more of the Rezko matter from us."