<h2>Abstract:</h2> A GLC method was developed for the measurement of steady-state levels of amitriptyline and nortriptyline in human plasma after therapeutic doses of amitriptyline. The drugs were extracted from alkalinized samples with heptane-3% isoamyl alcohol and back-extracted into 0.1 <i>N</i> HCl. After subsequent extraction into ether, the drugs were analyzed by GLC. The method is accurate, specific, and sensitive, being capable of measuring concentrations as low as 25 ng/ml of these drugs. After 6 days of amitriptyline administration (75 mg/day), levels of amitriptyline and nortriptyline in three subjects were approximately 40–90 and 40 ng/ml, respectively, 12 hr after the last dose.