Résumé : Wheat germ agglutinin, but not concanavalin A or soybean lectin, inhibited the basal-and stimulated-adenylate cyclase activity which was present in a plasma membrane preparation from the rat pancreas. The inhibition by wheat germ agglutinin was rapid and sustained. It was of the non-competitive type and never exceeded 20% for Gpp (NH) p- and NaF-stimulated adenylate cyclase activity. The inhibition of secretin-stimulated activity was also non-competitive but more pronounced (57% inhibition at a wheat germ agglutinin concentration of 20 microgram/ml). For the C-terminal octapeptide of cholecystokinin-pancreozymin (OC-PZ)-stimulated cyclase, the inhibition amounted to 68% and was of a mixed type (both competitive and non-competitive). This last observation might be explained by the competitive inhibition exerted by wheat germ agglutinin on the binding of peptides of the OC-PZ family to their membrane specific receptors. The various inhibitory effects of wheat germ agglutinin were completely suppressed by incubating the membranes in the presence of ovomucoid, a N-acetyl-D-glucosamine rich glycoprotein. The possible functional implication of these results is discussed.