Goreisan, a well-known hydrostatic modulating formulation, is used clinically in the treatment of edematous disorders. In this study, in order to clarify hydrostatic modulation in the intestine, we analyzed the effect of Goreisan in an experimental diarrhea model created with the single oral pretreatment of magnesium sulfate in mice. Ninjinto (166 mg/kg, p.o.) did not lead to improvements in this model, whereas Goreisan (133 mg/kg, p. o.) significantly abated the diarrhea.The warm Goreisan extraction (at 37 , for 0.5 hr) showed anti-diarrheal activity that was significantly stronger than the decoction. On investigating the anti-diarrheal activity of Goreisan by comparing the difference in crude drugs made from Atractylodis Rhizoma (Byakujutsu) and Atractylodis Lanceae Rhizoma (Sojutsu), no distinction between Byakujutsu-Goreisan and Sojutsu-Goreisan was recognized. Atractylodis Rhizoma, Polyporus, Poria, and Cinnamomi Cortex, which were administered singly, showed anti-diarrheal activities, but these were weak in comparison with Goreisan. Concoctions in which either Atractylodis Rhizoma, Polyporus, Poria, Alismatis Rhizoma, or Cinnamomi Cortex were omitted from Goreisan showed decreased anti-diarrheal activity as compared with Goreisan. The anti-diarrheal activity was clearly lower in the concoctions of warm extractions whereby the five kinds of crude drugs were extracted separately, compared with the warm extraction of Goreisan in which all crude drugs were extracted simultaneously.These findings suggest that the anti-diarrheal activity of Goreisan in this model was not dependent on a specific crude drug, it being optimal to extract the five kinds of crude drug simultaneously.