Plasma drug levels and urinary metabolites were measured in a volunteer for 28 h after ingestion of amitriptyline hydrochloride or amitriptyline N-oxide (amitriptylinoxide) equivalent to 100 mg of amitriptyline base. The N-oxide initially produced high plasma levels and 15% of the dose was excreted unchanged within 14 h. From comparison of the metabolite excretions, it can be concluded that about 70% of the dose was reduced at the N-oxide group, while comparison of the areas under the plasma group, while comparison of the areas under the plasma level-time curves for amitriptyline pointed to a 55% reduction to the amine. Less drowsiness was experienced after ingesting the N-oxide, and there was no depressive mood.