The most crucial time for close co-operation between clinical research and marketing research is during phase II and early phase III of clinical development. In these phases of development it is necessary to compare the new substance with similar drugs which are already on the market and with other competitors in different phases of clinical development. These comparisons are necessary in order to decide whether or not to continue development and, if so, to choose the very best marketing strategy. In combination with a preparation phase, the conjoint measurement method is a prime example of a productive collaborative effort between clinical research and marketing research. The preparation phase is a selection of most relevant attributes via in-depth interviews with pharmaceutical and medical opinion leaders in different countries. In this connection it is helpful for the marketing research agency to work together with a CRO (Clinical Research Organisation) using their knowledge of clinical research and their experience concerning contacts with possible opinion leaders. The evaluation phase is a conjoint measurement which is able to supply information about the ranking of importance of the attributes of the substances via conjoint measurement.