The dilemma of ceteris-paribus-tests and decisions is demonstrated. The classical solution, the regional test market, offers only unsatisfactory results. The requirements of a timely instrument, which can test the total marketing-mix, are more extensive. With the, for Europe unique, micro test market 'Behavior Scan' we succeeded in meeting these requirements. After introducing the instrument, our two years' experience with 'Behavior Scan' in Germany and an outlook to its further development are presented.