One Expert Systems in Medicine. - 1. Medical reasoning and artificial intelligence: general presentation of the problem. - 2. Representation and use of the knowledge. - Two Study of an Expert System. - 3. The SPHINX system. - 4. Examples of applications. - 5. The SPHINX system environment. - Three Validation. - 6. Validation of the expert systems. - 7. A crucial problem: validation of the knowledge base. - 8. Validation of a SPHINX knowledge base: some supplementary elements. - Appendix 1 Representation and use of knowledge: symbolic logic. - Appendix 2 Representation and use of knowledge: fuzzy sets and fuzzy logic. - Appendix 3 LISP coding of the MYCIN rules. - Appendix 4 Bayes' theorem and credibility factors. - Appendix 5 Other medical systems which employ artificial intelligence methods. - References. Language: English