The method being introduced here was developed by Infratest, Munich. The first section is devoted to the requisites of applications with which marketing models have to comply if they are to meet the requirements of the user. The second and third sections deal with the development of the model approach. The model is strictly speaking a dynamic and open one. Both environmental influences and the competitive conditions are simultaneously taken into account. The market is essentially described by three moduli of elasticity. Whereas the alpha values describe the competitive conditions, the beta values measure the success of the marketing strategy. Finally, the factor of inertia describes the sensitivity of the market to marketing within a lapse of time. The fourth section is devoted to a case study taken from the consumer market. In addition to a brief interpretation of the results, forecasts and possibilities for simulation are presented with the aid of the model. The reliability of the model parameter was tested here. Moreover, the findings were not computed for all of the eight periods investigated, but only for a shorter period of time. The marketing criterion of the periods not included was then "forecast" on the basis of the Model 369 parameter. The values forecast could now be compared with the values actually measured. When the Model 369 runs, including six periods, and the two periods were forecast, the result was throughout one of a high degree of reliability. On the basis of the forecasted values, it was also possible to compute various simulations for different marketing strategies and to examine their effects on the marketing success of all products.