One Expert Systems in Medicine.- 1. Medical reasoning and artificial 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 validation of the knowledge base.- 8. Validation of a SPHINX knowledge some supplementary elements.- Appendix 1 Representation and use of symbolic logic.- Appendix 2 Representation and use of 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.