Abstract: A stabilizer for driving and radially stabilizing a drill bit. The stabilizer has a fluid passage therethrough for passage of drilling fluid to the drill bit. The stabilizer includes radially extendable wedge-like members for stabilizing abutment thereof with a borehole wall; means affected by drilling fluid pressure or spring tension for controlling extension and retraction of the wedge-like members; and, inclined slide surfaces for frictional interaction with the wedge-like members to prevent radial movement of said stabilizer relative to a borehole.