1. The action of adrenaline, noradrenaline and efferent sympathetic fibres on the smooth muscle of the lower oesophageal sphincter (l.o.s.) was studied in vivo on the anaesthetized cat and in vitro with the sucrose gap method. 2. Adrenaline and noradrenaline produce a marked depolarization of the circular muscle of the l.o.s. This effect is suppressed by dihydroergotamine or phentolamine, and greatly reduced by atropine; it remains unaltered by hexamethonium. 3. Sympathetic fibres are excitatory for the l.o.s. They come from the stellate ganglion or run along the splanchnic nerve: the fibres arising from the stellate ganglion (mainly by the cardiac branch of the ganglion) join the vagus nerve at the thoracic level; the fibres running along the splanchnic nerve pass through the coeliac ganglion without synapsing; their cellular bodies lie probably in the ganglia of the sympathetic chain. 4. Repetitive stimulation (20--40 Hz) of these fibres induce, with a latency of 5--8 sec, a sustained or rhythmic contraction of the l.o.s. This response is suppressed by dihydroergotamine, and greatly reduced by atropine, while hexamethonium has no effect. 5. Stimulation of sympathetic fibres induces a facilitation of the vagal excitatory responses and an inhibition of the vagal inhibitory responses of the l.o.s. 6. Our data show that the sympathetic response of the l.o.s. results from the stimulation of adrenergic receptors which are located not only on muscular fibres but also, and chiefly, on intrinsic neurones. Thus, the sympathetic control of the l.o.s. is mainly exerted through cholinergic myenteric neurones which could be excited either directly or indirectly by inhibition of inhibitory intrinsic neurones.