Although complaints of excessive "gas" symptoms are frequently encountered in clinical practice, the physiologic and pathophysiologic grounds of flatus events are poorly understood, partly because of the social taboos associated with the topic and partly because of technical difficulties in measuring flatus. For these reasons, we studied the colorectal and anal motor events occurring during artificially evoked flatus events and compared them to those that occurred spontaneously. Five healthy male volunteers were studied by multilumen probes placed in the left colon and rectum and across the anal canal, to observe the flatus-related motor events that occurred after instillation of air into the colon. Flatus-related spontaneously occurring motor events were also checked in 24-hr motility tracings obtained in three patients with functional bowel disorders. Analysis of the tracings showed that both artificially induced and spontaneously occurring flatus-related motor phenomena were characterized by colonic propagated contractions associated with a rise in rectal pressure and early relaxation of the anal sphincter, in a sequence resembling that observed following swallowing. Spontaneous flatus events were associated with colonic waves of lesser amplitude than those following insufflation of air into the colon.