Abstract: A circulation tool 10 for use downhole in a well includes a housing 12 having one or more bypass ports 16 for circulation between a bore in the housing and an annulus surrounding the housing. A sleeve 68 is axially movable within the housing, and axially spaced seals 70, 74 seal between the sleeve and the housing when the sleeve is in the closed position. A ball 52 is rotatably mounted to the sleeve, and includes a seat 54 about a central bore 55 in the ball for engagement with a plug. When the sleeve closes off the circulation ports 16, the ball is rotated to the open position with a substantially full bore diameter.