Schoeneweis and righthander Doug Nickle were obtained in exchange for pitchers Gary Glover, Scott Dunn, and Tim Bittner. The addition of Schoeneweis gives the White Sox a lefthanded option out of the bullpen other than Damaso Marte.
Schoeneweis, 29, is 1-1 with a 3.96 ERA in 39 relief appearances this season. He owns a 1.31 ERA over his last 14 appearances and lefthanded hitters are just 14-for-77 (.182) against him with no homers.
"We had a very short list of guys we thought could fit into our situation right now and in the future," said General Manager Kenny Williams of Schoeneweis, who is arbitration eligible after this season. "He was obviously on that list."
The White Sox entered play Tuesday four games behind Kansas City in the AL West. They beat the Royals Tuesday night, 9-6.