Antidepressant Activity of Proproten-100 (antibodies to brain-specific S100 protein in ultralow doses) in patients with stage II alcohol dependence and alcohol withdrawal syndrome was studied in an open comparative clinical trial. The tricyclic antidepressant amitriptyline and benzodiazepine tranquilizer phenazepam served as reference preparations. Anxiolytic activity of Proproten-100 was highly competitive with that of phenazepam. Proproten-100 produced a stronger thymoleptic effect than amitriptyline. The preparation possessed activating properties, affected alcohol addiction, and did not cause side effects. Proproten-100 should undergo clinical tests during the therapy of neurotic, neurosis-like, and subdepressive borderline disorders.