In this paper we discuss a simple model for an interactive consultation system for medical applications. That system was developed to provide consultative advice on diagnosis of arthritis, but it could be easily applied to a different class of diseases. We examine in particular how the determination of the appropriate sequence of diagnostic tests that have to be performed on the patient can be optimised by the use of a decision table, in which the medical knowledge is shown. We begin with a review of features which were seen to be essential to a consultation system for medical applications and we suggest how these requirements imply program design criteria. This is followed by a formal explanation of the proposed model and its fundamental assumptions. The last part of the paper is then devoted to a report of our experience with the experimental computer system.