The role of the autonomic nervous system in control of the acute and the late-phase of insulin secretion was studied in mongrel dogs before and after bilateral severance of the vagus, splanchnic, and vagus plus splanchnic nerves. Glucose-stimulated acute insulin secretion increased after splanchnicotomy or transection of both autonomic nerves but remained unchanged after vagotomy alone. Late-phase insulin secretion was not altered by transection of any of the nerves alone or in combination; similar results were obtained as to fasting insulin levels. In contrast, fasting glycemia was increased after vagotomy and decreased after splanchnicotomy. These findings disclose tonic sympathetic and parasympathetic influences on blood glucose basal concentration and indicate an acute inhibitory role of the sympathetic system on insulin secretion.