Abstract Effects of synthetic peptides belonging to the CCK/gastrin family (CCK-39, CCK-8, G/CCK-4, G-17ns) on amylase release in dog pancreatic acini have been measured and correlated with binding of three radio-labelled CCK/gastrin peptides: 125I-BH-(Thr,Nle)-CCK-9, 125I-BH-(2–17)G-17ns and 125I-BH-G/CCK-4 prepared by conjugation of the peptides to iodinated Bolton-Hunter reagent and purified by reverse-phase-HPLC. All the CCK/gastrin peptides produced the same maximal amylase release response. Half-maximal responses (D 50) were obtained with 2 · 10 −10 M CCK-8; 6 · 10 −10 M CCK-39; 10 −7 M G.17 ns and 2 · 10 −6 M G/CCK-4. Dose-response curves for G-17 ns and G/CCK-4 were similar in configuration but not parallel with those for CCK-8 and CCK-39. Binding studies with 125I-BH(Thr,Nle)-CCK-9 demonstrated the presence of specific CCK receptors on dog pancreatic acini. There was a good correlation between receptor occupancy by CCK-8 and CCK-39 and amylase stimulation since maximal amylase stimulation was achieved when 40–50% of high affinity receptors were occupied. In contrast, a saturation of these receptors was required for maximal stimulation by G-17 ns and G/CCK-4 suggesting the existence of a fraction of receptors that can be occupied by G-17 ns and G/CCK-4 without stimulation of amylase release. Binding studies with labelled (2–17)-G-17 ns and G/CCK-4 confirmed the presence of high affinity sites for G-17 ns and G/CCK-4. These sites were not related to amylase release. This study points out a possible species specificity of biological action of gastrin/CCK peptides on pancreatic exocrine secretion in higher mammals.