Changes in blood pressure, heart rate, hematocrit, O₂ consumption, blood glucose, lactate, pyruvate and FFA during intravenous adrenaline infusion alone and after pre-treatment with alprenolol (Aptin^®), a beta-adrenergic receptor blocker, were studied in four healthy fasting male subjects according to double-blind technique with saline infusions as control. Adrenaline alone caused increases in heart rate, hematocrit and systolic blood pressure and a decrease in diastolic pressure. After alprenolol, adrenaline infusion gave a decrease in heart rate with an increase in both systolic and diastolic blood pressure, while the hematocrit was unchanged. The adrenaline infusion caused significant rises in all the metabolic variables studied. Pre-treatment with alprenolol abolished all these rises with the exception of blood glucose.