After oral administration of a therapeutic dosage (400 mg) Mefexamide (I), six excretion products were detected in human urine and subsequently identified by GC/MS and TLC: in addition to the unchanged drug (I) in the acidic extracted urine without hydrolysis p-methoxiphenoxiaceticacid-methylester (II) and p-methoxiphenoxiaceticacid (III) were detected; the latter two and p-hydroxyanisole (IV) were also found in the acidic extract after hydrolysis (with hydrochloric acid or enzymatic). In the alkaline urine extract besides the unchanged drug (I) and the main metabolite V (partially described previously by Forist et al. [8]1), metabolite VI, which occurred only in very small amounts, could be detected. Additionally, 2-diethylaminoethylamine (VII) was identified as an artifact in the alkaline extract after acidic hydrolysis. Hydrolysis of mefexamide with hydrochloric acid led to substances II, III, IV, and VII. For the main metabolite V, a synthesis route is described. Approximately 15% of the administered drug was recovered in the 24-h urine; substances I and V could be detected a least 72h after application.