provoked an equivalent increase in plasma non-esterified fatty acids (+ 100%). Procaterol, but not yohimbine, induced hyperglycaemia (+ 120%). Plasma insulin was weakly enhanced by yohimbine (+ 120%) as compared to the increase given by procaterol (+ 500%). 4 Both drugs stimulated sympathetic nervous system activity, as indicated by the increased plasma noradrenaline concentration, but only yohimbine increased the plasma adrenaline level. 5 Cardiovascular measurements indicated that procaterol strongly enhances heart rate and transiently decreases mean blood pressure. Yohimbine exhibits a weaker effect on heart rate and slightly increases mean blood pressure. 6 The present work clearly indicates that lipid mobilization is enhanced during fasting in the dog by selective fl2-adrenoceptor stimulation or by Cc2-adrenoceptor blockade. This enhanced lipolytic effect may result either from a direct action of the drugs on the adrenoceptors of fat cells or from an activation of the sympathetic nervous system. Procaterol suffers major limitations since it strongly increases heart rate, immunoreactive insulin and glycaemia. On the other hand, yohimbine induces only minor modifications both in cardiovascular and endocrinological parameters.