Expert system evaluation comprises verification, validation and user acceptance testing. The nature of expert systems requires that they be elvaluated carefully, and that detailed methodologies for their development he devised. This paper attempts to give practical guidance for the e\,aluation phase of' expert system de\-elopment. Empirical and logical e~alrrution methods are surveyed, and both types of method are applied in an evaluation case study. This case study provides insights as to the relative effectiveness of the methods. and demonstrates that empirical and logical testing are complementary to each other. The paper concludes that any eiwluation methodology should incorporate both types of method, and presents prescwptions and an orrtline for such a methodology, which combines the methods for maximum effectiveness.