A randomized prospective clinical trial has been performed to determine the effect of temporary immobilization of the shoulder on wound drainage following radical mastectomy. In 64 patients admitted to the trial the mean volume of drainage was reduced by 40 per cent in those who had shoulder movement restricted for the first 7 days after operation when compared with the group in whom early arm exercises were encouraged. The mean drainage time was reduced by 29 per cent. Shoulder immobilization did not result in increased shoulder stiffness, although there was an increased incidence of mild lymphoedema of the arm.