Exposito, 25, is a career .268/.324/.420 hitter over seven Minor League seasons in Boston's system. He was the club's 31st-round selection in the 2005 First-Year Player Draft.
To make room for Exposito on the 40-man roster, the Orioles designated infielder Josh Bell for assignment. The 25-year-old switch-hitter, currently at Triple-A Norfolk, batted .200/.221/.264 in 79 games with the Orioles in 2010 and '11. He was acquired on July 30, 2009, in exchange for left-hander George Sherrill.
The move will give the Orioles organizational depth, as they were thin at the catching position behind starter Matt Wieters. Ronny Paulino, who arrived at camp three weeks late, made the club as the backup with Taylor Teagarden on the disabled list.
"He' a catcher, we are a little thin there," manager Buck Showalter said of Exposito. "I'm not sure exactly where they are going to send him or what the plan is, but we got some good reports on him. He's a good addition to once again strengthen our 40-man roster. That's something we didn't have."
Brittany Ghiroli is a reporter for MLB.com. Read her blog, Britt's Bird Watch, and follow her on Twitter @britt_ghiroli. This story was not subject to the approval of Major League Baseball or its clubs.