Therapeutic montitoring of drugs is a well established clinical 1001. However, the state of art is somewhat less advanced for psychotrpoic agents than it is for other classes of drugs, for several reasons. Most psychotropics have large volumes of distribution and achieve relatively low plasma concentrations following therapeutic doses. Many have one or more active metabolites. As a consequene, the analytical methodologies are often complex and not always reliable; well-controlled clinical studies are difficult to perform; and therapeutic ranges have been difficult to establish. Despite these limitations, prudent and selective monitoring of serum drug concentrations, particularly of the tricyclic antidepressants can be helpful in clinical management. This paper presents an overview of clinical and mothodological issues surrounding the utility of blood level measurement.