The behavioral pattern of an animal is influenced by endogenous and endogenous stimuli such as humoral secretion, neurohumoral transmitters, drugs, light and environmental change. It has teen known that adenosine is a normal constituent of brain, and has sedative or hypnotic effects and anticonvulsant effects, inhibiting the spontaneous firing of cells in the brain via membrane adenosine receptors. Recent studies suggest that the excitatory responses to xanthines in the CNS might be related to the competitive antagonism of xanthines to adenosine. This study was undertaken to Investigate the effects of adenosine and the CNS stimulants such as picrotoxin, strychnine and caffeine on the spontaneous activity of mire, and to examine the influence of adenosine on the seizures induced by large doses of CNS stimulants. Subjects were 20 ~ 30 g adult mice, and the spontaneous activity was measured using the Selective Activity Meter after intraperitoneal injection of adenosine (10 mg/kg), caffeine (100 mg/kg), strychnine(0.2 mg/kg) or picrotoxin(0.5 mg/kg) with or without adenosine pretreatment. The seizures were induced with caffeine(200, 250 and 300 mg/kg), strychnine(1.25 and 1.5 mg/kg) or picrotoxin(10 and 15 mg/kg). The results are summarized as follows : 1) The spontaneous activity in mite was significantly inhibited between 10 and 20 minutes after adenosine treatment. 2) Caffeine and picrotoxin increased the motor activity significantly while strychnine had no effect on the activity. 3) The ambulatory activity in the caffeine, strychnine and picrotoxin treated groups was significantly inhibited by adenosine pretreatment. 4) The seizures were observed with caffeine(200, 250 and 300 m9/kg), strychnine(1.25 and 1.5 mg/kg) or picrotoxin(10 and 15 mg/kg). The caffeine induced seizures were inhibited by adenosine pretreatment, but the strychnine or picrotoxin induced seizures were not affected.