Two cases of pancreatic polypeptide cell hyperplasia were obtained by operation. The first case exhibited adenocarcinoma of the stomach with metastases to the neck lymph nodes and pancreatic polypeptide hypersecretion. Pancreatic polypeptide cell hyperplasia was confirmed by the immunoperoxidase method and by the elevated level of pancreatic polypeptide in the pancreatic extracts and in the circulating blood. There was no watery diarrhea syndrome. The second case presented with persistent watery diarrhea of two and one-half year duration, and the resected pancreas contained extremely large atypical islets, exclusively composed of pancreatic polypeptide cells. It is speculated that in some cases pancreatic polypeptide oversecretion may be causative for pseudo-Verner-Morrison syndrome in the absence of ulcer of carcinoma in the upper gastrointestinal tract.