Abstract: A horizontal drilling machine for directionally drilling a drill string into the ground. The drill string includes a plurality of elongated members threaded together in an end-to-end relationship. The drilling machine includes a track, a rotational driver mounted on the track, and a thrust mechanism for propelling the rotational driver along the track. The rotational driver is used to rotate the drill string in forward and reverse directions about a longitudinal axis of the drill string. The drill string is rotated in the forward direction to thread the elongated members together, and rotated in the reverse direction to unthread the elongated members from one another. Rods of the drilling machine have surface irregularities for mixing or agitating drilling fluid within the bore.