In this paper, we discuss the usability of an antibiotics therapy adviser, with a broad, complex spectrum of functions which we have developed within the ICONS project. We present the architecture of the system, case-based reasoning methods used, steps and results of medical evaluations, which are concerning the quality of the recommended therapies, the user friendliness of the system and the interpretation of laboratory results. Furthermore, we discuss problems of transferability of such a system from one site to another as well as problems of local susceptibility patterns and individual dose regimens.