The effects of propranolol, given by close arterial injection, on the reflex vasodilatation induced in the atropinized isolated gracilis muscle by rapid i.v. administration of norepinephrine were studied in dogs. The integrated areas of vasodilatation were significantly reduced after treatment with propranolol. Thus the conclusion was that adrenergic beta-receptors participate in the reflex vasodilatation, although how they act needs further elucidation.