The effect of abduction and adduction of the arm on the position of central venous catheters inserted via cubital veins was studied in 41 surgical patients. The location of the catheter tip and the abduction-adduction angle were measured from x-ray pictures. With adduction, the catheter always advanced inwards, the maximal movement being 9.5 cm. The average displacement varied from 2.0 cm to 3.3 cm and there was a statistically significant correlation (P less than 0.001; r = 0.831) between the advancement of the catheter tip and the abduction-adduction angle. There was no correlation between tip displacement and change in central venous pressure.