Since the 1950s, an American company named IMS developed specialised market research for pharmaceutical companies. By quantifying global drug sales on both regional and national levels IMS offered an important tool to major drug companies' marketing strategies. From then on, it was possible to know the approximate market size of each therapeutic group, each subgroup and even of each dosage form of a product and its competitors. Combined with information on prescription habits and physicians' diagnostic choices, these new computer-based projections promised to make drug markets manageable. These new knowledge technologies gave pharmaceutical companies an important advantage over health insurance or regulatory bodies that did not have access to these numbers. In my contribution I present IMS Health's market research tools and the results they produced. IMS Health's story will be embedded in a larger history of drug costs and consumption. Based on IMS Health's archival documents I will show how knowledge on drug markets became indispensable for pharmaceutical markets and health policies.