Some new alkaloids (gardneramine, gardnerine, gardnutine, and hydroxygardnutine) were isolated from a domestic plant, Gardneria nutans SIEB. et ZUCC. (Japanese name "Horai-kazura") and their structures were determined. The central nerve effect of gardneramine and gardnerine was examined in mice. Acute toxicity of gardneramine is lower than that of gardnerine. Depression of spontaneous motor activity, weak antagonistic effect on hypermotility induced by methamphetamine, motor incoordination, prolongation of sleeping duration induced by hexobarbital, and hypothermic effect were found in both alkaloids, gardneramine having a greater effect. Analgesic effect was found by the writhing test in acetic acid and tail pain test in both alkaloids but this effect may be very weak because of their low potency in the latter test. Anticonvulsive effect to seizure induced by maximal electroshock, pentetrazol, and strychnine was not found in either alkaloid but convulsion induced by nicotine was antagonized by them. In electrocorticographic examination in rabbits with chronically implanted electrodes, gardneramine produced slow waves and shortness of duration of arousal response to acoustic stimulation. From these results, it may be concluded that gardneramine has a mild central depressive effect and gardnerine has a weaker effect.