The ganglion blocking site of gardneramine (GA) and hirsutine (HS) was studied in the dog urinary bladder in an in situ preparation. GA and HS selectively inhibited the DMPP-induced contraction without having an antagonistic effect on the McN-A-343-induced and acetylcholine-induced contraction. In addition, since GA and HS showed a local anesthetic action weaker than that of procaine, the effect of procaine was studied on the same preparation. Procaine inhibited the McN-A-343-induced contraction, and it slightly inhibited the DMPP-induced and acetylcholine-induced contraction. From these findings, it is concluded that GA and HS inhibited the ganglionic transmission of the dog urinary bladder and that the blockade of the nicotinic receptor played a main role.