These guidelines suggest how clinical chemists may promote rational laboratory use by critically evaluating the tests they offer. This may be done by documenting the clinical uses and limitations of tests in the same way that properly written up method descriptions outline analytical procedures in a particular laboratory. This information can then be promoted on result report forms, in discussion or through investigational protocols or clinical guidelines. For these to be of value they should be the result of clinical and laboratory input reflecting the local practice and facilities. They should be clearly written, easily accessible to the users and updated whenever there is a change of methodology or clinical practice. Much can be achieved by applying common sense to common knowledge and laboratories of all sizes can prepare their own material. However, national scientific societies and other professional organisations can assist local endeavour by avoiding and disseminating educational material on test evaluation, selection and use.