A method of determining a direction of introduction and tracing an introduction path along the direction of introduction of a medical instrument into an organism, with the use of an ultrasound imaging machine suitable for 3D-imaging, comprising the steps of scanning a larger volume of the organism with a 3D-scanning unit of the ultrasound imaging machine, determining the direction of introduction of the medical instrument with a guiding device coupled to the 3D-scanning unit, the direction of introduction being determined by the position of the guiding device relative to the 3D-scanning unit, generating a B-image of an intended introduction range in a sectional plane within which the introduction path runs, aligning the 3D-scanning unit with the guiding device coupled thereto with the sectional plane in the generated B-image, observing the introduction path in an image display of the sectional plane, the sectional plane being located by predeterminable selection criteria and the introduction path being virtually displayed, and selecting a prismatic or cylindrical part of the larger volume for display in a 3D-image in which the introduction path may be observed, the primsmatic or cylindrical part of the larger volume having a main axis coaxial with the direction of introduction.