A rigid analogue of promazine, 3-(dimethylamino)-1,2,3,4-tetrahydroazepino[3,2,1-kl]phenothiazine (1), was prepared by reductive amination of the corresponding ketone 4. An X-ray crystallographic study revealed that the seven-membered ring of the hydrochloride salt of 1 exists as a half-chair-like form with the dimethylammonium group in an equatorial-like conformation. Compound 1 was approximately one-half as active as promazine as an inhibitor of [3H]spiperone binding in rat corpus striatal homogenates. In homogenates obtained from calf caudate tissue, however, 1 was only about one-twentieth as active as promazine as an inhibitor of [3H] spiperone binding. As a stimulator of homovanilic acid (HVA) synthesis in rat corpus striatum in vivo, it was about one-tenth as active as promazine.