Since there has been no report on the quaternary bases of Corydalis platycarpa MAKINO, this quaternary base portion was reduced with sodium borohydride and dl-tetrahydrocorysamine, dl-tetrahydropalmatine, and dl-tetrahydrojatrorrhizine were isolated and identified. dl-Corybulbine was also isolated and identified with the sample prepared from dl-tetrahydrojatrorrhizine. dl-Isocorybulbine was also synthesized. dl-Corybulbine obtained here is a reduced compound and should be present in the plant as the quaternary base dehydrocorybulbine. This is the first time that the base was obtained in this reduced form.