A case with the clinical appearance of WDHA syndrome is described in which serum concentrations of the newly recognized hormonal principle pancreatic polypeptide (PP) were highly elevated, while plasma levels of vasoactive intestinal peptide were within the normal range. The symptoms of the patient seem to be derived from the high levels of circulating PP, as illustrated by an improvement after resection of liver metastases accompanied by a marked decrease of serum PP concentration. Streptozotocin treatment was without effect upon the watery diarrhoea, and PP levels also remained unchanged during medical treatment. The appearance of a PP-secreting tumour leading to a clinical WDHA syndrome widens the spectrum of hormone assays that have to be performed in these patients.