Human interdigestive intestinal motility follows a circadian rhythm with reduced nocturnal activity, but circadian pancreatic exocrine secretion is unknown. To determine whether circadian changes in interdigestive pancreatic secretion occur and are associated with motor events, pancreatic enzyme outputs, proximal jejunal motility, and plasma pancreatic polypeptide concentrations were measured during consecutive daytime and nighttime periods (12 h each) in seven healthy volunteers using orojejunal multilumen intubation. Studies were randomly started in the morning or evening. Nocturnally, motility decreased (motor quiescence: 67 +/- 22 vs. 146 +/- 37 min; motility index: 3.59 +/- 0.33 vs. 2.78 +/- 0.40 mmHg/min; both P < 0.05) but amylase output increased (273 +/- 78 vs. 384 +/- 100 U/min; P < 0.05) and protease output remained unchanged (P > 0.05); consequently, enzyme/motility ratio increased. Amylase outputs were always lowest during phase I. Motor but not pancreatic circadian activities were associated with sleep. Pancreatic polypeptide plasma concentrations were unchanged. Consequently, intestinal motor and pancreatic exocrine functions may have different circadian rhythms, i.e., decreased motor and stable secretory activity during the night. However, the association between individual phases of interdigestive motor and secretory activity is preserved. The nocturnal increase in enzyme/motility ratio is probably not caused by increased cholinergic tone.