Abstract: A down-the-hole hammer drill having a reverse circulation system which conducts pressurized air downwardly to a lower cutting face of a drill bit. The air travels across the cutting face and upwardly through a central exhaust passage. The air is conducted to the cutting face through longitudinal and lateral passages in the bit which are kept isolated from the environment surrounding the bit so that no appreciable amount of pressurized air can escape, and so that the passages do not become clogged with dirt. The drill bit comprises upper and lower pieces. Upper sections of the longitudinal passages are formed in the upper piece, and lower sections of the longitudinal passages are formed in the lower piece.