Diagnostic decision support systems are ready for prime time. We used them in a general medical clinic and found that they could suggest new diagnostic possibilities, focus thinking about clinical problems, and serve as a tool for recertification preparation. In addition, we have found diagnostic decision support systems useful for the novice clinician (fourth-year medical students and interns). These tools serve as a reminder system for learners, suggesting questions to ask the patient, physical exam components to complete, and tests to order. The novice clinician may also use these systems in preparing case presentations. The systems reviewed vary in the ways we described earlier, and there is no one "best buy." Which program is right for you depends on how much detail you want, whether you prefer a CD or internet format, and in what setting you practice. Demos are available from most vendors: Try them out, make a choice, and get on with the business of enhanced diagnostic decision making.