Abstract: A transformable circulation tool for reversing the path of drilling fluid at the drill bit without removing the drill string from the borehole annulus is provided by a substantially hollow body having a chamber with external ports disposed between a section of the body having a through passage and a by-pass passage in combination with a diverter mounted on a telescoping member having means for engaging the body during drilling and disengaging the body for rotation of the diverter with respect to each of the passages. A seal is rotatably mounted to the substantially hollow body between the ports to divide the well borehole into an upper conventional flow portion and a lower portion where the flow of the drilling fluid can be reversed upon command from the surface.