The clinical use of image analysis requires on the one hand a knowledge of pathology, physiology and other medical fields, and on the other hand expertise in image processing techniques. Because of the increasing complexity, these techniques are not often employed by clinical users, who want to focus on interpreting results rather than focusing on the choice of a specific package, the way it operates and the underlying processes. Thus it is of prime importance to clinical users to have at their disposal a system which can accept their clinical knowledge as input, then convert it into an appropriate mathematical language, process it, and finally return the results to them in a clinically intelligible fashion. The concept of an 'intelligent system' interface between medical users and applications has been developed, which we have termed an Interactive Quantitation Support System (IQSS). Such a system translates clinical knowledge into symbolic descriptions and transmits them to the software application. IQSS manages the dialogue between user and application, as well as error handling. A prototype of the user interface has been developed based on a client/server architecture and a data-oriented environment. Early in its development, this IQSS has been tested in prototype form to perform a three-dimensional registration of multimodality images.