The ultrasound reflecting characteristics of a needle (1) or catheter are enhanced by a bubble-filled plastics stylet (2, 72), which inserted in the bore (10) of the needle or catheter and is effectively acoustically coupled to the inside of the needle or catheter. This may be done in several different ways. In one arrangement, a liquid (3) or the like is introduced between the outside of the stylet (2) and the inside of the needle (1) or catheter. In another arrangement, the stylet (72) is of a compressible material having a natural external diameter greater than the internal diameter of the needle or catheter so that the stylet is in compression within the needle or catheter. The stylet (72) may be stretched longitudinally by means of an extension rod (76) for insertion.
