Protein kinase from the bull myocardium tissue was separated by means of the stepped gradient of buffer concentrations on DEAE-cellulose. Sensitivity of the obtained fractions to cAMP was studied. Protein kinase isolated at elution by 0.3 M potassium-phosphate buffer from DEAE-cellulose is less sensitive to cAMP than protein kinase isolated according to Kuo. A decrease in the content of cAMP is established in the tissues of the skeletal muscles and adrenals of rats after long physical loading. No statistically significant changes are found in the level of cAMP under the same conditions in the myocardium and brain tissues.