Alterations in the electrical activity of the stomach were studied in 40 unanesthetized dogs with intact vagal innervation, with selective proximal vagotomy (SPV) and with truncal vagotomy (TV) using a chronically implanted unipolar needle electrodes. The basic electrical rhythm (BER) of the normal canine stomach occurred regularly in the frequency of 4.5 to 5.5 cycles per minutes with a waxing and waning of initial and second potentials repeated in every 5 to 6 minutes. After SPV, irregular BER was observed occasionally within a few days postoperatively. After TV, irregularity of BER was more marked and frequent for the first 2 weeks. Subcutaneous administration of bethanechol chloride or histamine decreased the frequency of regular BER and increased the magnitude of second potentials equally in any dog of the control, SPV and TV groups. Similar changes were observed after feeding of the canned meat. Insulin-induced hypoglycemia increased the magnitude of antral second potentials in either control or SPV dogs. In contrast, TV dogs revealed repetition of initial potentials shortly after intravenous adminstration of insulin, but failed to show any changes relevant to hypoglycemia.