N-Acyl-γ-D-glutamyl peptide derivatives containing a C-terminal small fragment of cholecystokinin were prepared and their effects on gastric secretion were investigated. PhCO-D-Glu(Phe-NH₂)-NPr₂ and PhCO-D-Glu(Asp-Phe-NH₂)-NPr₂ inhibited gastric secretion, while PhCO-D-Glu(Met-Asp-Phe-NH₂)-NPr₂ and PhCO-D-Glu(Trp-Met-Asp-Phe-NH₂)-NPr₂ stimulated gastric secretion. The substitution of the acyl function at the N-terminal of PhCO-D-Glu(Phe-NH₂)-NPr₂ affected the activity. Z-D-Glu(Phe-NH₂)-NPr₂, 4-chlorobenzoyl-D-Glu-(Phe-NH₂)-NPr₂ and isonicotinoyl-D-Glu(Phe-NH₂)-NPr₂ were found to have more potent inhibitory activity against gastric secretion than proglumide (PhCO-DL-Glu-NPr₂).