Turnbow was 0-1 with a 15.63 ERA in eight games this season and gave up six runs in two-thirds of an inning at Chicago Wednesday.
He had 39 saves in 2005 and 24 the following year, when he was picked for the NL All-Star team. But he suddenly lost his form at midseason in 2006.
After converting 51 or 55 save chances at the start of his career, he went 0-6 with a 13.06 ERA from July 1 on in 2006 and lost his closer's job to Francisco Cordero. Turnbow was 4-5 with a 4.63 ERA as a setup man last year.
Milwaukee designated the 30-year-old right-hander for assignment as is responsible for the remainder of his $3.2 million salary this year. The Brewers have 10 days to trade him, place him on unconditional release waivers or send him outright to the minors.
To take Turnbow's place, Milwaukee recalled outfielder Joe Dillon from Triple-A Nashville.