Vasoactive intestinal peptide (VIP) and the newly discovered pancreatic polypeptide (PP), both having been proposed as pathogenetic factors in the watery diarrhea syndrome (WDRA), were intravenously infused into rats in order to study the effect on small bowel propulsion. Simultaneously with the infusion of hormone, radioactive test substance was continuously infused into the duodenum of the conscious animal through a permanent catheter. By recording the distribution of radioactivity along the excised gastrointestinal tract, analyses of small bowel propulsion were possible. After infusion of VIP small bowel transit time was significantly prolonged, and the local propagation velocity was retarded both in the proximal and the distal part of the small bowel. PP did not alter small bowel populations. The heavily retarded transport rate after VIP is a propulsive dysfunction and not inconsistent with the clinical sign of diarrhea.