The Brewers made the move Wednesday. Their bullpen has been a sore spot early this season.
The 31-year-old Rodriguez played for Milwaukee the last year and a half. He pitched 78 games last season, going 2-7 with three saves and a 4.38 ERA.
Rodriguez set the single-season saves record with 62 in 2008 with the Angels.
The Brewers got K-Rod from the New York Mets in a trade in July 2011. He is a four-time All-Star and has led the league in saves three times.
Milwaukee has used Rodriguez as a setup man, rather than as a closer.