Thompson began this year with the Royals, and he was 0-4 with a 6.41 ERA in 16 games before being designated for assignment earlier this month. He refused his Minor League assignment, and Astros assistant general manager Ricky Bennett signed him to add depth and stability to the staff.
Thompson is 21-21 with a 4.46 ERA in 201 career games, mostly as a reliever. His best season came in 2007, when he was 8-6 with a 4.73 ERA in 44 games for the Cardinals, including 17 starts. He appeared in eight playoff games for the Cardinals in 2005-06, including one World Series game in '06.
Thompson, 28, was 0-1 with a 5.40 ERA in three starts for the Express, allowing one walk and 16 hits in 11 2/3 innings pitched.