Culture of mouse mammary gland cells was treated with beta-agonist isoproterenol to result in dose dependent increase in protein. Propranolol, beta-antagonist, blocked this effect of isoproterenol. According to electron microscopic analysis, application of isoproterenol leads to disappearance of vesicles from apical zones of the secretory cells, and to increase in casein micelles in alveolar lumen. As follows from the obtained data, catecholamines play part in regulation of mammary gland activity, stimulating process (via beta-adrenoreceptors) of protein extraction from secretory cells of the mouse mammary gland.