40 749 RP, an N-methyl-2-(2-pyridyl)-2,3,4,5-tetrahydro-2-thiophene carbothioamide derivative, is already known as a potent gastric antisecretory agent in animals and in man. In order to determine its duration of action, its activity was investigated on Histalog-stimulated gastric acid secretion in 6 healthy volunteers. The efficacy of a 2 mg/kg dose, compared with that of placebo, was potent, and remained the same when the drug was ingested 6 h before stimulation instead of 1 h. The duration of action of 40 749 RP is therefore longer than 6 h.