We discuss a reminder system that automatically interprets the results of routine biochemical tests for thyroid hormones. We measured serum levels of thyroid stimulating hormone (TSH), total thyroxin (TT4), triiodothyronine (TT3), thyroxin-binding globulin (TBG), and thyrotropin-releasing hormone (TRH)-stimulated TSH (sTSH [1,2]). The developed knowledge base was used to compare and rate these results with a defined set of diagnoses. Various forms of altered thyroid and/or pituitary function [3-8] were considered. For a given combination of test results, the reminder system classified the entered diagnoses as "obligatory", "possible", or 'excluded". The knowledge base is now part of a medical documentation system at the outpatient thyroid department of the Division of Endocrinology and Metabolism of the Vienna General Hospital. We report an evaluation performed after six months of operation. Although further improvement will be required, the knowledge-based reminder system in its present form is capable of improving the quality of manually entered diagnoses.