Electromyographic activity of the sphincter of Oddi was recorded by means of bipolar suction electrodes applied to the rabbit, in which the sphincter of Oddi is easily identifiable and independent of the duodenal musculature. Seventy animals were investigated (20 in vitro and 50 in vivo). The bile duct was catheterized so that the pressure could be recorded. The sphincteric traces show basal activity consisting of bursts of 1-8 spike potentials which recur every 3-5 seconds on average and are accompanied by a transient rise in biliary pressure. The patterns are different from those recorded for the duodenum, the activity of which does not affect biliary pressure. On the basis of these findings, it can be asserted that the sphincter of Oddi plays a part in biliary flow apart from any duodenal muscular action. This method has made it possible to study the behavior of the sphincter of Oddi under the influence of certain physical agents or drugs. Within certain limits, the frequency and amplitude of the spike potentials increase with temperature and the rise in biliary perfusion pressure. Acetylcholine, prostigmin and morphine hydrochloride increase the frequency and amplitude of the spike potentials and shorten the resting intervals. Inhaled amyl nitrite and intravenous hexamethonium reduce electrical activity. The depressant effect of atropine is much less marked in the rabbit. Intravenous administration of alcohol results in a substantial increase in the electrical activity of the sphincter and in biliary pressure. This effect is reduced by vagotomy and suppressed by hexamethonium.