It is Proposed in the Present study to investigate the effects of TTX intravenously or intrahypothalamically administered on the arterial blood pressure and respiration and also to explorc effect of intrahypothalamically administered TTX on the pressor responses to electrical stimulation in the hypothalamus. The results obtained are as follows; 1) The pressor responses to electrical stimulation in the hypothalamus were markedly reduced after administration of TTX. In the 0.01 μg/kg of TTX administered group, the pressor responses were almost abolished in 6 minutes and there was no tendency toward recovery throughout the experiment. 2) In 0.01 μg/kg of TTX administered group, the mean arterial blood pressure and heart rate-were gradually reduced while there was a transient increase in respiratory rate followed by slow recovery thereafter. On the other hand no changes in arterial blood pressure, heart rate an4 respiration were observed in 0.005 μg/kg TTX administered group. 3) Following intravenous administration of 1 μg/kg TTX, the arterial blood pressure and heart rate were slowly reduced by 60 minutes while no marked changes were found in respiration. From the results of present study it is strongly suggested that TTX exerts its depressant effect not only on peripheral nerves but also on central nervous system.