An endosteal guide pin for preparing a guide path for the implantation of a pedicle or orthopaedic screw into a patient's bone. The pin has a head intended to be provisionally implanted in a bone and a guide rod, coaxial with and rigidly secured to the head, ending in a free end intended to be at least level with the skin surface of the patient when the pin is in the implanted position in the bone. The pin has a first coupling part intended at least to secure the pin to and release the pin from at least one portion of a positioning trocar and a second coupling part intended at least to secure the pin to a removal trocar. Also, a trocar for positioning a guide pin, which trocar incorporates the guide pin, and to a trocar for removing the pin.