A series of medical instruments can be made with the use of shape memory tube with a transformation temperature that is above or below the ambient temperature. In the first case, the material behaves with the shape memory effect and in the second case the behavior is superelastic. The wall of the tube has been provided with a plurality of slots in specific places, often near or at the distal end of the instrument, and in specific arrangements which allow local variations in diameter, shape, and/or length. These variations can either be caused by the memory effect during temperature change or by superelastic behavior during change of the mechanical influences on the memory metal by the surrounding material.