Miles had been on the disabled list since June 29 with an injured elbow. He was back in the starting lineup at shortstop for the final game of a series against the Cincinnati Reds.
Miles is batting .203 with no homers and 46 RBI this season. He also was on the disabled list from May 27 to June 10 with a strained right shoulder.
The Cubs have moved into first place in the NL Central with a strong run since the All-Star break, inching ahead of St. Louis. They've done it without catcher Geovany Soto, who has been sidelined since June 7 by strained muscles in his left side.
General manager Jim Hendry watched Soto play on a rehab stint in the minors this week and thought he was ready to be activated. Soto is expected to rejoin the team Friday in Colorado for the start of a three-game series.
With Soto out, Koyie Hill has started 26 consecutive games, the first Cubs catcher to do that since Jody Davis started 38 straight in 1986. Manager Lou Piniella said Hill will continue to play regularly after Soto returns.
"He'll do some catching as we get Soto in shape," Piniella said. "I know the record [with Hill behind the plate]. He's done a really nice job. We appreciate it."
Reliever Jeff Stevens was optioned to Triple-A Iowa on Wednesday to open a roster spot for Miles. The right-hander had no record and a 2.84 ERA in five games with the Cubs.
Ryan, the former Blue Jays closer, signed a minor league deal with Chicago on July 16 and appeared in five games for Iowa. The 33-year-old reliever was 1-1 with a 6.53 ERA when Toronto released him on July 8.
"Ryan asked for his release today," Hendry said. "He handled himself great. He just didn't feel like he was going to be able to help us this year. He just wanted to go home and regroup. His velocity wasn't there."