Studies were performed in anesthetized opossums to investigate the electrical activity that may characterize the lower esophageal sphincter. The stomach and lower end of the esophagus were immobilized on a specially prepared stage to eliminate movement artifacts. Extracellular electrical activity was recorded with bipolar needle electrodes. The sphincter pressure was measured with a continuously perfused catheter system. The lower esophageal sphincter showed continuous spike activity with or without phasic variations in their occurrence. The usual frequency of the spikes was 20 to 50 per min, and their duration was 81.2 +/- 8.9 msec (mean +/- SE). The spike potentials ceased with esophageal distention, which also caused a fall in the sphincter pressure. The spikes were abolished by isoproterenol and they increased with bethanechol. Correlation of the spike activity with the pressure revealed that the sphincter pressure was higher when the spike potentials were present, but a major part of the pressure existed in the absence of any spike activity. These studies show that: (1) the oppossum lower esophageal sphincter is characterized by continuous spike potentials, and (2) the major fraction of the basal pressure is, however, independent of the spike potentials.