Dehydrocorydaline, an alkaloid from Corydalis bulbosa possessing anti-ulceric activity, was labeled by methyl-14C at position 13, and its disposition and metabolism were studied in mice and rats after oral (50 mg/kg) or intravenous (6.8 mg/kg) administration. Blood levels were as low as 0.5 (mice) and 0.06 (rats) microgram eq./ml at maximum, conceivably due to its poor absorption from digestive tracts. Radiometric and autoradiographic studies after oral administration of 14C-dehydrocorydaline revealed that appreciable radioactivity was distributed in rather restricted organs, namely, digestive tracts, liver and kidney. Comparison of distribution with that after intravenous administration suggested that the compound is subject to the significant first pass effect by the liver. The distribution pattern of radioactivity in the liver was heterogeneous regardless to administration routes. Radiometry and autoradiography also revealed that the disposition did not differ significantly from each other in normal rats and those with experimentally induced gastric ulcer. Excretion of radioactivity occurred largely in feces. Excretion via urine and bile was quite minor. Metabolite analysis suggested that dehydrocorydaline was metabolized by O-demethylation and subsequent conjugation with glucuronic acid. However, metabolites were minor relative to the unchanged compound.