CADIAG-1 is a medical expert system, based on a symbolic logic representation of medical relationships. Strong relationships such as confirming, excluding or obligatory occurrence are applied to confirm or exclude diagnoses. Weak relationships are represented by facultative and not confirming relationships (FN-relationships). Diagnostic hypotheses are established by systematic combination of symptoms showing FN-relationships. CADIAG-2, a medical expert system based on fuzzy set theory and fuzzy logic, allows detailed specification of medical relationships. Here the diagnostic process also provides confirmed and excluded diagnoses as well as diagnostic hypotheses. Hypotheses are calculated by considering fuzzy relationships between medical entities. 426 cases with rheumatic and 47 cases with pancreatic diseases were tested. For CADIAG-1, the overall accuracy for confirmation and hypothesis generation is calculated with 91.1% for rheumatic diseases and 100% for pancreatic diseases. CADIAG-2 reached an overall accuracy of 93.7% for rheumatic cases and 91.5% for pancreatic cases.