Insulin hypoglycemia provokes an increase in the intensity of Parkinsonian tremor, probably by increasing endogenous adrenaline (epinephrine) production. Intravenous epinephrine also increases tremor. The effect of hypoglycemia and epinephrine can be abolished by [beta]-adrenergic blockade. Mental stress also increases tremor, but this response is not influenced by [beta]-blockade. The effect of emotional and mental stress on parkinsonian tremor is possibly mediated by release of endogenous epinephrine and by direct influence of the prefrontal cortex on brainstem reticular formation.