The Web-Based Artificial Intelligence for Diagnostic Use (WeAidU) system is a support system providing near instantaneous professional aid in clinical decision making. The system involves neural networks trained to interpret myocardial perfusion scintigrams, and enhance the effectiveness of clinical decision making when it comes to coronary artery disease. The system is designed to work on the Internet in a client/server setup . The usability of the system is evaluated. The evaluation result is related to two previous evaluations. A link is made from evaluation results to the way the system is designed and developed. It is observed that some of the usability problems found are tied to the development process. Usability inspections locate a number of possible problem areas when it comes to the user interaction. At the same time the user's assessment of usability is satisfactory or even high. This is most likely explained by the novel nature of this computer support and a very committed user group. Clinical physiology is acknowledged to be a computerized field, where physician's acceptability and use of computers is fairly high. It is observed that the development team's, in this particular context, favored a view of usability as a quality of the product before the view of usability as integrated in the development process/product. A more integrated view of usability is suggested to remove usability errors and integration barriers, and to help the system better fit into the physician's daily routines.