PURPOSE: Interstitial cells of Cajal (ICC) play a core function in colonic motility as a pacemaker by regulating the slow wave. We intended to investigate the electrophysiological characteristics of the circular smooth muscle in the human colon, especially in Koreans. METHODS: Colon tissues were obtained from patients undergoing an elective colectomy for non-obstructive lesions. Tissues were immediately stored in oxygenated Krebs-Ringer's bicarbonate solution, and conventional microelectrode recordings of the colonic circular muscle were done from muscle cells. RESULTS: The trans-membrane potentials from 100 tissues were recorded. Regular slow-wave patterns were observed in 36 patients, and 64 patients showed irregular wave patterns. In the tissues exhibiting regular slow-wave patterns, 20 tissues were recorded from the proximal colon and 16 from the distal colon. The frequency of the slow wave from the proximal part was significantly higher than that from the distal part. The resting membrane potential, the upstroke amplitude, the spike amplitude, and the maximal rate of rise showed no significant difference between the two parts, but the time to reach half amplitude did show a significant difference between the two parts. No significant differences in parameters were observed based on the patients' demographics such as sex and age (younger or older than 60). We were able to divide the irregular waves into 3 groups. Irregular slow waves were observed in 35 tissues, irregular slow waves mixed with spike waves were observed in 26 tissues, and spike waves alone were observed in 3 tissues. CONCLUSION: We analyzed the electrophysiological characteristics of the human colonic circular smooth muscle, especially those of the slow wave originating from ICC of patients who had not been pretreated with drugs.