Little attention has been paid before to the diagnostic efficiency of clinical chemical tests. In view of the ever increasing number of clinical chemical analyses and the critical development of expenses in medical health care, an evaluation of this aspect of clinical chemical analyses seems to be urgently required. Various new methods, that might be used, are reviewed. Qualitative and quantiative tests, and the so-called multiple analysis are discussed as examples of clinical chemical methods. The necessary mathematical treatments (use of the Bayes theorem, information theory, likelihood ratio method, and others) are illustrated with the aid of worked examples. A new cost-effectiveness analysis of clinical chemical data is suggested.