The hard-throwing righty had been suffering from a right groin strain. Aardsma made two rehab appearances for Triple-A Pawtucket before being cleared to return.
"Physically, everything is awesome," Aardsma said. "The two rehab outings went well. I'm very happy with those."
In his last outing before going on the DL, it was clear that Aardsma was being hindered by the injury. The proof was in the radar gun.
But that was no longer the case at Pawtucket.
"Yeah, he did good," said Red Sox manager Terry Francona. "His velocity was better, and he said he was feeling free and easy where he's not feeling it. He'll go out here and throw a light bullpen [session], just a little touch and feel after we stretch."
It was nice timing for Aardsma, who got to return against his former team -- the White Sox.
"I'm as excited as you could imagine," Aardsma said. "It was one of those things, I wanted to get back, get healthy. That was key. To have it come down to this series, right now, that's kind of big. But I'm just happy I'm healthy. I'm happy I'm here, and I'm ready to go."
Aardsma has plenty of familiarity with Chicago, having pitched for the Cubs in 2006 and the White Sox last year.
"I loved the White Sox while I was here, the whole organization," said Aardsma. "Obviously some places are better for some people than others. It didn't work out here. I'm definitely exited to be back. I want to get out there and beat these guys."
Aardsma is 3-2 with a 2.75 ERA in 38 games for the Red Sox this season.
Ian Browne is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.