The position of the tip of a central venous catheter inserted through an arm vein is not influenced by the arm or by the vein chosen. There may be some advantage in inserting the catheter with the arm at the patient's side, although there seems to be no benefit from turning the patient's head towards the side of insertion. Because the most common malposition from an apparently uneventful insertion is due to the catheter tip entering the internal jugular vein, neck compression has been established as a useful test. If the catheter tip is well into the internal jugular vein, compression on that side of the neck should cause a rise in the recorded pressure of 10 or more cm H20. This rise should not occur on compression of the other side of the neck. We wish to emphasize that it is important to confirm radiographically the position of the catheter tip.