A downhole tool which can perform a task in a well bore, such as circulating fluid radially from the tool. The function is selectively performed by virtue of a sleeve moving within a central bore of the tool. Movement of the sleeve is effected by dropping a ball through a ball seat on the sleeve. Movement of the sleeve is controlled by an index sleeve such that the tool can be cycled back to the first operating position by dropping identical balls through the sleeve. Embodiments are described wherein the balls are deformable, the seat is deformable and the seat provides a helical channel through which the ball passes.