Bile acid output in the duodenum was studied in relation to the interdigestive migrating motor complex in normal subjects and in cholecystectomy patients. In normal volunteers the bile acid output preceding a duodenal activity front (217 +/- 89 mumol/30 min) was 374% of the output following a front (58 +/- 24 mumol/30 min) (P < 0.05). In cholecystectomy patients the prefront output (354 +/- 64 mumol/30 min) was 195% of the value obtained in the postfront period (234 +/- 59 mumol/30 min) (P < 0.05). These results indicate that the bile acid output into the duodenum during the interdigestive phase in fluctuating in accordance with the interdigestive motility complex.