Effective marketing plans are key to product success in today's mass markets. And whether they are effective or not is - to a large extend - determined by the consumer and his reaction to it. For the marketers of consumer goods this means they have to guaranty that each variable of that marketing plan is accepted on its own and, moreover, in combination with the other variables of it. The individual factors of marketing plans have been checked separately by most marketers already. However, it has not been recognized that there are interactions between them when they are combined to one single marketing plan. There can, e.g., be supportive effects between certain tactical elements of a plan and its more strategical parts. It is also possible that specific factors become ineffective in combination with certain others. And, not to forget, the plan of one brand might have an effect on or be effected by that of another brand. All of this can only be found out in-market. Therefore, a new research tool was developed that allows marketing plans to be tested in-market without, however, running the financial risk of a regional or even national roll-out: the experimental micro test market. The following paper is going to demonstrate the relevance and results of in-market testing with the aid of two anonymized cases that have been carried out in GfK-BehaviorScan, the first micro test market in Europe with targetable TV system that allows the inclusion of TV advertising into marketing plan research.