We defined duodenal ulcers (DUs) not healed within 3 months with H2-antagonists as "intractable", because the recurrence rate of these DUs is higher than that of DUs healed within the same periods, and etiological differences are suggested to exist among these two groups. To verify the pathophysiological differences, gastric analysis including modified sham-feeding (MSF) were performed in 1 2 intractable, 10 tractable DUs and 5 healthy controls. By MSF stimulation, acid output increased in all subjects and the mean acid output of MSF amounted to about 60% of the tetragastrin maximum.Meanacid output of intractable DU cases was significantly higher than the controls in any stimulatory state and was different only in MSF with tractable DU. No significant changes of serum gastrin were recognized during MSF and both serum pepsinogen I and II are higher in DU cases than the control in basal state, but the two DU groups show no significant difference or increase by MSF or gastrin stimulation. These data suggest that vagal activity of intractable DUs is higher than not only healthy subjects, but tractable DUs and participation of gastrin in the increase of acid output by MSF might be denied.