In dogs and rabbits anesthetized with pentobarbital sodium or urethane, respectively, the gastric mucosal blood flow was measured by the thermoelectrical method after intravenous administration of 3-(3, 4, 5-trimethoxybenzamido)piperidine(KU-54), an antiulcer drug. In the gastric corpus of rabbits, the maximal mucosal blood flow (11.9%) was attained within 1 min after KU-54(5 mg/kg i.v.) dosing and there was a prolonged increase during 8 min. Administration of KU-54 produced a transitory depression of the blood pressure by about 20%, and induced a beta-adrenergic-like action, presumably because both the blood pressure depression and the gastric mucosal blood flow increment were simultaneous in rabbits. This phenomenon was however, not abolished by pretreatment with propranolol, a beta-adrenergic blocker, therefore KU-54 may not be a beta-adrenergic blocking agent. Administration of gefarnate, a standard antiulcer drug, produced a slight increase in gastric mucosal blood flow and response to this drug was less than that seen with KU-54. Sulpiride, a standard antiulcer drug, two peaks on the gastric mucosal blood flow increment in rabbits and the pattern of blood flow increment differed from that seen with KU-54. The increment of gastric mucosal blood flow produced by KU-54 (5 mg/kg i.v.) was more successive in the gastric antrum than that in the gastric corpus. In fasting rabbits, the main period of gastric mucosal blood flow increment produced by KU-54 (5 mg/kg i.v.) was more successive than that seen in the non-fasting animals. In dogs, the maximal blood flow (16%) was observed at 7 min after KU-54 (5 mg/KG i.v.) dosing and there was a prolonged increase during 6 min.