A medical image workstation has been conceived and prototyped which is designed to act as a cooperative dialogue partner in a number of routinely performed tasks in diagnostic radiology. The system can automatically select relevant information (e.g., current and previous examinations, images, image sequences) and generate a meaningful and appropriate image arrangement on the display screen. This is shown to be an effective feature to simplify and speed up radiological image access and presentation. For many cases in diagnostic image reading, the users' interaction may be as simple as switching from one patient to the next. Furthermore, the installed mechanisms offer a solution for the automatic pre-fetching of images to avoid transmission delays in the course of diagnostic work sessions. The cooperative system response is based on explicit (formalized and computer-accessible) models of diagnostic information requirements. These models are context-dependent and take into account that diagnostic information needs vary with radiological work procedures, workstation users, and patient cases. Initial information requirement models have been acquired from expert radiologists in two European hospitals and were integrated in a cooperative workstation prototype. For the representation of models, rule-based and object-oriented techniques were applied. The rule base was designed with a distinct modular structure, separating between rule sets for general, task- and user-dependent information requirements. The paper reviews the objectives for the design of cooperative workstation user interfaces and describes the acquisition, structuring, formalization, and representation of context-dependent information requirement models. The rule-base is explained by examples. A layered workstation architecture consisting of model-, object-, and realtime-layer is presented. Difficulties in the implementation of cooperative workstations are discussed which point to future research topics and standardization activities.