The practicability of a method or of an apparatus is one of the "figures of merit" which are used by the clinical chemist to choose a method or an apparatus. Joined to the reliability and the efficiency, it has to be evaluated by different tests. Unfortunately, few reflections concern the definition of this criterion, which often is little discussed in the other divisions of the pure and applied chemistry. The clinical chemist is well suited to study and evaluate the practicability. The present paper attempts to define this criterion and to set the discussion of this question.