Abstract: A circulating tool for use in drilling a bore hole, the tool including a plurality of pistons which, by the activation of fluid pressure, move between a first configuration in which a side port of the tool is covered by a piston and a second configuration in which two adjacent pistons separate across the port to allow fluid to jet from the port. In the first configuration, the tool has a continuous cylindrical bore to allow the passage of other tools through the tool, while a flapper valve closes the bore in the second configuration to achieve maximum jetting of fluid from the tool. A third or intermediate configuration is also described so that the tool is operable to switch multiple times between the configurations via an indexing mechanism.