N-(Cis-2-phenyl-cyclopentyl)azacyclotridecan-2-imine-hydrochloride (MDL 12330A), considered an inhibitor of adenylyl cyclase, has been tested on the enzyme activity of neuronal and non-neuronal tissues from the freshwater snail Planorbarius corneus. The drug dose-dependently activates the basal as well as agonist-stimulated adenylyl cyclase in the ganglionic preparations, while it exerts an inhibitory effect on the enzyme present in the non-nervous tissues examined. SQ 22536 and forskolin, respectively an inhibitor and activator of adenylyl cyclase, behave as generally reported both in central and peripheral tissues of the snail. This is, to our knowledge, the first report of a stimulatory action of MDL 12330A on an adenylyl cyclase system.