Abstract The effect of total parenteral nutrition (TPN) in rats on a number of enteroendocrine cells was investigated. The rats were given a continuous intravenous infusion of basal TPN solution for 7 days. Samples from duodenum, jejunum and ileum were collected, immunostained and the immunoreactive cells quantified using a computerised morphometrics system. The endocrine cells containing somatostatin, cholecystokinin (CCK), gastric inhibitory polypeptide (GIP), neurotensin and enteroglucagon were investigated. The results demonstrated a significant reduction in the number of CCK cells in the duodenum and jejunum. In the ileum the neurotensin-immunoreactive cells were significantly increased in number ( P < 0.02). No change was seen in the number of cells immunostained for somatostatin, GIP or enteroglucagon. These data indicate that short term TPN has a definite effect on the enteroendocrine cell population which may be linked to the side effects of TPN seen in man.