The electromyographic activity of the large bowel was studied in patients suffering from aganglionic megacolon and in comparable normal infants and children, using of an intraluminal electrode. Graphs obtained in control children showed a basic electrical rhythm of 4-6 waves/min with bursts of high frequency spikes, 3-4/sec, superimposed on the top of the slow waves. The recordings in Hirschprung's disease showed an irregular basic electrical rhythm with waves of variable duration and no high frequency potentials, as long as the electrode was positioned in the aganglionic zone. As soon as the electrode was introduced further up into the normally innervated colon the graph became identical to that seen in the normal bowel. Intraluminal electromyography of the rectum and colon seems to be a suitable procedure to diagnose aganglionosis of the rectum and the extent of the lesion.