Tricyclamol is a quaternary ammonium compound, which is a crystalline odorless substance, readily soluble in water. It may be given by mouth or by subcutaneous injection. Tricyclamol was used for its spasmolytic action on smooth muscle. In animals it inhibits the spasmogenic effects of acetylcholine (ACh), carbachol, pilocarpine and barium chloride. In relaxing ACh-induced spasm of isolated rabbit ileum the activities of the dextro and laevo isomers of tricyclamol were approximately 0.006 and 2 times that of atropine sulphate respectively. Further, in inhibiting the stretch reflex of isolated guinea-pig ileum the laevo isomer was much more active than the dextro and about twice as potent as the racemate. Tricyclamol blocks the superior cervical ganglion. Tricyclamol chloride has a marked effect in reducing the motility of the stomach and duodenum, and to a far greater extent than the results produced by hyoscyamine. This action may be of value in controlling the pain of peptic ulceration, since it is likely that the pain, at least in part, is due to spasm.