Abstract: The present invention relates to a method and apparatus which provides proactive guidance to a surgeon for guiding the tip of a surgical instrument along a previously defined optimum path within the body of a mammal to a tumour or other target within the body. This path is subdivided into a plurality of sections extending from one intermediate point to another and an image is formed on the exposed surface of the body of the mammal upon which the surgeon is operating. The image is focused below the exposed surface and at the next intermediate point to be traversed along the path. The image provides the surgeon with vector information as to where he should direct the tip of the instrument. The image is preferably three or more overlapping dots of light from lasers which are directed at the intermediate point by motorised mountings under the control of a computer, the splay of the dots of light giving the surgeon the vector information.