Abstract: A method of drilling long and straight holes in rocks is based on the use of a drill rig which may be aligned by means of a laser beam and which comprises a hollow drill stem with a pressure device for guiding the drill stem in a correct direction on applying pressure against the wall of the drilled hole. The laser beam is sent into the hollow drill stem towards an optical detecting unit placed inside a hollow control arrangement joined into the drill stem behind its drill bit, the control arrangement being operated by means of signals from the detecting unit. The arrangement constituted a connecting piece of the drill stem and comprises a pressure device which is in contact with the wall of the hole. The optical detecting unit is arranged with free sight to the source of the laser beam as long as the drill stem is sufficiently straight.