Patent information users have access to a wide variety of patent databases from commercial providers and the patent offices which significantly differ in content and coverage. A clear distinction can be made between value-added and first level patent databases with respect to search precision and comprehensive retrieval. This article covers the results of a case study in the pharmaceutical field which directly compares first level patent data and value-added patent information of Chemical Abstracts Service and Thomson Scientific. The focus of the case study is to analyse the unique information provided by each file and put the different types of patent files into perspective. The analysis clearly demonstrates that the unique patent information of Derwent World Patents Index® (Derwent WPI) and the CAS suite of files is indispensable for any business critical search request.