The invention relates to a catheter system comprising a first, outer catheter (1) and a second catheter element contained in it, which can particularly be a guide wire (2). A respective active localizer (4, 5) is placed on the first and on the second catheter element (1, 2), for example sensors of a magnetic tracking system. The first catheter element (1) preferably has a fixing device (3), by means of which it can be fixed relative to the vascular system (7). If the guide wire (2) is, for example, to be navigated through a stenosis (6), the position of its localizer (5) relative to the localizer (4) is measured on the catheter element at rest (1), so that its position relative to the vessel (7) is known. Since interference factors such as organ movement balance each other during the measurement of the relative position of the localizers (4, 5), the navigation can be carried out with very high accuracy.
