Isolated gastric glands from the rabbit were used for studying the effect of catecholamines on the release of pepsinogen. Isoprenaline, adrenaline and noradrenaline stimulated pepsinogen release in a dose-dependent manner with similar maximal effects, but isoprenaline was significantly more potent than the other two agonists. The effect was mediated through beta-adrenoceptors, since the response was inhibited by the beta-adrenoceptor antagonist, propranolol, and since the alpha-adrenoceptor agonist, phenylephrine, was without effect in the concentration range 0.01 - 10 microM. Concentration-response curves for isoprenaline were shifted to the right in parallel by increasing doses of propranolol, and maximal response was not influenced by propranolol per se, which indicates a competitive type of antagonism. A Schild plot showed a pA2-value for propranolol of 7.70 and the slope of the regression line was 1.02. Studies with the beta 1-selective antagonist pafenolol and the beta 2-selective antagonist ICI 118.551 demonstrated that isoprenaline acted through beta 1-adrenoceptors. The results suggest an adrenergic component in the control of the peptic cells in rabbit gastric mucosa.