The development in the last eight years of various surgical technics directed toward alleviation of essential, or idiopathic, hypertension has renewed interest in the role of the sympathetic nervous system and its splanchnic divisions in regulation of blood pressure and their possible etiologic role in clinical hypertension. These surgical technics have been chiefly directed toward sympathetic denervation of the splanchnic area. It is difficult to evaluate the therapeutic effect of these procedures and even more difficult to estimate whether the improvements reported are related to an elimination of etiologic factors or to a direct effect produced by denervation of large vascular beds. The experiments to be considered in this study deal with an attempt to reexamine the role of the sympathetic nervous system and its splanchnic divisions in regulation of blood pressure. The possible role of the sympathetic system in the production of chronic neurogenic hypertension in man is also