Effects of various cathartics on charcoal transport, permeability of blood vessels and biogenic amines (serotonin (5-HT), histamine (His), polyamines) in the small intestine of mice were investigated. Diarrhea was induced in mice by oral administration of magnesium sulfate, mannitol, dioctyl sodium sulfosuccinate (DSS), castor oil and pilocarpine. In diarrhea following ingestion of magnesium sulfate and mannitol, vascular permeability in the intestinal membrane accompanied release of His from the small intestine, but such was not so when diarrhea was induced by DSS and castor oil. In diarrhea induced by various cathartics, 5-HT and His were apparently not related to intestinal motility. Thus, alteration in polyamine metabolism in the small intestine may exert an influence on transport of substances in cases of diarrhea in mice.