The antimuscarinic potency of dibenzepin (Noveril) was estimated by measuring (a) central in vivo effects in mice (antihypothermia and antitremor, both induced by oxotremorine), (b) peripheral in vivo activity (mydriasis caused by systemic administration of the drug), (c) the effects of dibenzepin on isolated smooth muscle from guinea pig ileum, and (d) in vitro determination of the affinity constant of dibezepine toward the muscarinic binding sites in whole mouse-brain homogenate. The data allowed the construction of a normalized antimuscarinic potency scale for some of the common tricyclic antidepressants. With a value of 1 for scopolamine, the following relative anticholinergic potencies were calculated: dibenzepin--1/600, nortriptylne--1/300, imipramine - 1/200, and amitriptyline - 1/75. These values suggest an explanation for the absence of clinically detectable anticholinergic side effects during treatment of depression with high doses of dibenzepin. Structural and spatial interrelations among various tricyclic antidepressants and scopolamine are discussed.