Peguero gives the team some added outfield depth with Michael Saunders battling a sore groin muscle. Casper Wells figures to be added as well, but he's not eligible to return until after Triple-A Tacoma's season ends on Monday because it hasn't been 10 days since he was sent down to make room for Franklin Gutierrez.
Peguero, 25, hit .285 with 21 home runs and 54 RBIs in 76 games with Tacoma. He also batted .146 in 41 at-bats in a brief stint with Seattle in July.
Ramirez, 22, was 6-3 with a 3.72 ERA in 15 starts with Tacoma. He posted an 0-2 record and 3.82 ERA in 11 games with the Mariners, including four starts before he went on the 15-day disabled list with a strained right elbow in early July.
Manager Eric Wedge said he wasn't sure yet whether Ramirez would be given any starts with the Mariners over the final month.
"We haven't had lengthy discussions about that yet," Wedge said prior to Saturday's game with the Angels. "He just started the other day. We'll use him today [out of the bullpen] if we have to. I'd like to stay away from him, but we felt like we needed to have another arm here, just in case."
The Mariners will bring more players up after Tacoma's season ends. Reliever Shawn Kelley and first baseman Mike Carp are two certain additions, but both have been dealing with injuries.
Kelley was hit in the elbow with a line drive in his last outing, so he was scheduled to throw an inning Saturday for Tacoma in order to make sure he's OK.
Carp is on a rehab assignment with the Rainiers as he recovers from a strained groin, but he had his best game Friday on a 3-for-6 night with a home run and double in a 19-3 win at Fresno.