The new long-acting somatostatin analogue octreotide was investigated for its influence on segretatagogue-stimulated human exocrine pancreatic secretion. Eighteen healthy volunteers participated in the study. During duodenal intubation with a background stimulation of either secretin 1 U. kg/h or secretin 1 U. kg/h + ceruletide, 120 ng. kg/h, octreotide was infused at doses of 5, 20 and 80 pg/h in a placebo-controlled randomized double-blind crossover trial. Duodenal juice samples were collected in 10-min intervals, and amylase, trypsin, chymotrypsin, and bicarbonate were measured in the individual fractions. 59%, trypsin between 28 and 72%, chymotrypsin between 55 and 70%, and bicarbonate between 0 and 31 % with 5, 20 and 80 pg/h octreotide.During secretin and ceruletide stimulation, amylase was significantly inhibited by 84%, 789'0, 819'0, trypsin by 76%, 55 %, 52%, chymotrypsin by 77%, 55 %, 60%, and bicarbonate by 25 %, XI%, 19% with 5,2O, and 80pg/h octreotide, respectively (all decreases P < 0.05).During secretin stimulation, amylase was inhibited between 4 1 and Correspondence to : Professor Dr med. P. Malfertheiner, Universitat Ulm, Abteilung Innere Medizin 11,