In this paper we are going to expound a control method which enables us to measure the effectiveness of promotional actions. We will be illustrating its application through an actual example of gauging a typical promotion, 'sampling'. The suggested method is based on a follow-up review of purchasing evolvement through a specifically designed panel, which begins before the actual promotion and continues thereafter long enough to allow an aver- age of three product purchases to take place. In order to determine the actual effect of the promotion over total product sales evolvement, product consumption is also followed by a standard consumer panel not affected by the promotion. This technique, quite simple in design, can be very useful not only to quantify the effectiveness of the promotion generally assumed up to now but also to select among its various alternatives.