Summary Somatostatin is a regulatory peptide implicated in the control of cellular proliferation in epithelial tissues and this regulation may occur directly via membrane bound receptor activation. The aim of this study was to investigate somatostatin binding in human gastrointestinal cancer and normal mucosa. Plasma membranes were prepared from specimens of tumour and normal mucosa from 51 patients undergoing surgical resection for malignancy (28 gastric, 23 (Horowitz et al., 1975;Higgins et al., 1941;Crile, 1957;Osei et al., 1985). There is, however, no currently defined role for endocrine therapy in non-endocrine gastrointestinal cancer. Surgical intervention is the most effective treatment for this condition and, even then, can only afford a 'cure' in early disease. Advanced tumours are associated with a poor prognosis, marginally improved by chemotherapeutic regimens. Any benefit from systemic therapy is usually abrogated by systemic toxicity (Rake et al., 1979;Engstrom et al., 1985;Bleiberg, 1990). For this reason a non-toxic, effective, treatment modality would be of value to improve the outlook for those patients with advanced disease.There is increasing evidence that tumours arising from the gastrointestinal tract are, at least in part, hormone dependent. Numerous hormones have now been implicated in the pathogenesis and development of gastrointestinal malignancy, including gastrin, epidermal growth factor, enteropancreatic hormones and oestrogenic steroids (Sirinek et al., 1985;Watson et al., 1988;Li et al., 1980;Howatson & Carter, 1985;McMichael et al., 1980). These findings, together with the observation that transformed gut epithelial cells may retain functional hormone receptors , have suggested a role for hormonal manipulation in these malignancies.Somatostatin and its analogues are good candidates for use as endocrine agents in the treatment of gastrointestinal cancer. The native peptide is widely distributed in the body and, amongst its many inhibitory actions, has a putative role as an anti-proliferative agent in both normal (Lehy et al., 1979) and malignant tissue. The mechanisms involved in this anti-proliferative action have not, as yet, been confirmed. Both the native peptide and its analogues act at the somatotrophs of the anterior pituitary suppressing growth hormone production and release (Adrian et al., 1981). This may influence the proliferation of target tissues directly or may result in a substantial reduction in local growth factor release (Kirkegaard et al., 1984 (Reubi et al., 1987a;Reubi et al., 1987b;Reubi et al., 1990;Ikuyama et al., 1985). Somatostatin (1981). In brief, frozen tumour and mucosal samples were mechanically pulverised and homogenised on ice in homogenising buffer (sucrose 250 mM, KCI 25 mM and MgCl2 10 mM in Tris-HCI 50 mM; pH 7.4) at 10,000 r.p.m. in short bursts for 2 min using an Ultraturrax T25 homogeniser (Scientific