Tricylic antidepressants (TCAs) have been widely used in clinical practice for the treatment of depression. Patients often show variability in clinical response to these drugs, so each dose must be individually determined for maximum effectiveness and safety. Differences in an individual's metabolism and the frequently encountered noncompliance with dose schedules, however, complicate matters. The measurement of serum levels is an effective way of determining if a patient is receiving an adequate therapeutic dose of a specific TCA.This application brief details an effective extraction procedure and the chromatographic conditions for the determination of commonly used antidepressant in serum using an internal standard.