Abstract. To study the effect of cholinergic stimulation on catecholamine release, methacholine, a choline ester, was injected im into normal subjects. Significant increases in plasma norpinephrine and plasma epinephrine concentrations were observed in response to methacholine administration with significant haemodynamic changes, but there was no correlation between the rise in plasma catecholamines and the haemodynamic changes. These results suggest that the increases in plasma catecholamines induced by methacholine did not result from reflex responses to haemodynamic changes and thus could be a direct effect of methacholine on sympathetic nerves and the adrenal medulla.