A standard duodenal perfusion/aspiration technique was used to continuously monitor biliary and pancreatic excretion in young healthy human subjects, and the excretory patterns were examined by Fourier power spectral analysis. Experiments were carried out in the fasting state, either without or during a continuous parenteral (i.v.) stimulation by secretin and the cholecystokinin analogue ceruletide. The duodenal content aspirated was either discarded after sampling or reinfused into the jejunum. In the fasting state, significant biliary and pancreatic excretion was detected, fluctuating with a periodicity of about 60 min. During parenteral infusion with ceruletide/secretin, to simulate a postprandial state, the rate of biliary and pancreatic excretion increased as compared with fasting levels alone (basal levels). A dominant period of about 60 min was still detected but second periods of approximately 45 min and approximately 95 min, respectively, were also observed. The peak power and the total power of the biliary excretion signals were reduced. Reinfusion of aspirated duodenal fluid into the intestine (jejunum) led to a further decrease in peak power and total power of the known biliary signals. Trypsin excretion into the duodenum revealed mainly insignificant changes in peak and total power upon hormone stimulation despite a definite increase in total amount of trypsin excreted. The results indicate that parenteral ceruletide/secretin stimulation has a stabilizing effect on biliary excretion in man, and that reinfusion of aspirated duodenal content into the intestine further stabilizes the excretion.