RECONSIDER is a computer program that is designed to be a diagnostic aid in general internal medicine. The paper begins with an easily understandable explanation of the medical diagnosis process and describes how the capabilities of RECONSIDER fit into this process. An experiment designed to show how well RECONSIDER meets its objective of suggesting diagnoses to the physician is described in detail. The criterion was whether or not the ultimate correct diagnosis was among the possibilities suggested by the program. The authors candidly discuss both the benefits and shortcomings of the program and of the experiment, so the paper should be very helpful to researchers in medical decision making.