After another month of rehab, Paxton's starting to build his arm strength back up and the bullpen session will be another step along that way.
"I'm feeling really good," the 25-year-old said Monday. "I've been working real hard here trying to get myself ready again. Today was probably the best day I've had just in letting it go. I'm just working on getting my timing down and today was probably the best that's felt. One day at a time."
Manager Lloyd McClendon isn't putting a timetable on Paxton's return.
"He's doing extremely well," McClendon said. "How far away he is, I can't answer that. We'll just have to wait and see."
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB as well as his Mariners Musings blog. This story was not subject to the approval of Major League Baseball or its clubs.