The use of tricyclic antidepressant drugs is becoming increasingly prevalent for the treatment of depressed patients. It has been suggested that, analogous to many other drug substances, the tricyclic drugs exhibit clinical effectiveness within a defined therapeutic concentration range (1–10). Very recently, both Dito (11) and Orsulak and Schildkraut (12) have summarized the usefulness of measuring serum concentrations of these drugs. These authors suggest that knowledge of the plasma concentrations of these drugs aid the physician in determining patient compliance and initiating the best possible drug treatment.