To measure simultaneously motility and flow of intestinal contents, a multilumen polyvinyl tube was passed by mouth in 10 healthy volunteers. Motility was recorded at five sites, spanning 100 cm of tube, to allow recognition of migrating motor complexes during fasting and during their disruption by food. Loci were designated as jejunal, ileal, and terminal ileal, as judged by length of tube in the intestine and by fluoroscopy. Flow of intestinal contents was measured by indicator (phenolsulfonphthalein) dilution over a 20-cm segment; flow was related to motility at the perfusion site. A liquid test meal of 400 ml and 600 kcal, containing polyethylene glycol 4000, was eaten after 6 h of fasting. During fasting, flow of intestinal contents was intermittent at all levels and varied with the presence of or absence of the activity front ("phase 3" of the migrating motor complex). The activity-front periods contributed 50% of total flow, but occupied less than one-third of the total recording time. Flow corrected for time was significantly greater with the presence of activity front than with phases 1 or 2 of the migrating motor complex (p less than 0.001). In addition, of 45 increments in flow of greater than 0.75 ml . min-1, the majority (82%) were associated with an activity front. The flow rate increased promptly after a meal and fluctuated markedly during the postprandial period in most studies. By the time migrating motor complex had returned, more than 90% of meal marker (polyethylene glycol) was accounted for in intestinal aspirates. In contrast, only 56%-73% of marker was recovered postprandially in those studies in which the migrating motor complex had not returned by the time the study was terminated. Thus, flow of intestinal content is largely intermittent during fasting, peaks of flow being associated with passage of the activity front of the migrating motor complex; on the other hand, half the fasting flow is unassociated with the activity front. Reappearance of the migrating motor complex at any level after a liquid test meal signals clearing of the liquid meal from the more proximal intestine.