This paper describes two rule based decision support systems. The first system is used to screen incoming test requests for adequacy on the basis of signs and symptoms volunteered by the requesting GPs. The system was tested using a database of 794 requests for a TSH test. About 17% of the test requests were correctly identified as unnecessary. In total, 0.5% of the tests were incorrectly labelled as unnecessary. This concerned 4% of the patients that appeared to have hyperthyroidism and 23% of the patients that appeared to have hypothyroidism on the basis of TSH and FT4 results. The other system is a rule-based clinical decision support system for the requesting of laboratory investigations, originally designed for use at a hospital within the UK, that was implemented in a predominantly French-speaking hospital in Belgium. This involved the modification of the system to allow multilingual operation, and also the implementation of a completely new set of investigation protocols. The purpose of this study was to assess the transferability, both of the system itself, and of its benefits. The system was introduced gradually and has only recently been in full operation. However, the findings from the first months of routine use of the system indicate that the transfer of the system to a different clinical environment has been successful. Although it is too early to assess fully the impact on laboratory utilization, the clinicians believe that it is improving the appropriateness of investigations.