Gastrin exerts a trophic influence on various regions of the gastrointestinal (GI) tract and this has led to an interest in its potential role in the growth of Gl tumours. There is little evidence that elevated circulating levels of gastrin predispose to colonie tumours. However, the hormone can be detected within some colonie tumour tissues and a possible paracrine or autocrine role has been proposed. At present, evidence for such a role is conflicting, as is the evidence that colonie tumour cells possess receptors for the mature hormone. Colonie tumours have been found to contain much higher concentrations of incompletely processed gastrin precursors such as glycine extended gastrin and recent studies indicate that they may exert trophic effects mediated by specific receptors. Further studies of this are required. Whether specific hormone receptor antagonists will have a role in the clinical management of colonie tumours remains unclear.