A newly synthesized compound, BTM-1042 (cis-(--)-2,3-dihydro-3-(4-methyl-piperazinyl)methyl-2-phenyl-1,5-benzothiazepin-4(5H)-one dihydrochloride) depressed the twitch responses of the ileum from guinea pig to electrical stimulation at 0.1 Hz. This inhibitory action of BTM-1042 was not influenced by naloxone, a narcotic antagonist. BTM-1042 proved to be almost as active as atropine on electrically stimulated ileum. BTM-1042 also blocked muscarinic receptors but the potency was about 1/3 of that of atropine. The responses of the ileum of guinea pig to nicotine and 5-hydroxytryptamine also were inhibited by BTM-1042. However, BTM-1042 did not influence the release of transmitters from motor, sympathetic, nonadrenergic inhibitory (or purinergic nerve), noncholinergic excitatory nerves and responses of various smooth muscles mediated through drug receptors, except for the acetylcholine receptor. Spontaneous movement of the unanaesthetized rabbit stomach was dose dependently depressed by BTM-1042 (0.04--0.2 mg/kg, i.v.). The potency ratio for BTM-1042 relative to atropine was 7.4. BTM-1042 is apparently a new type of potent, antispasmodic drug.