THE importance of the presence of choline derivatives for the maintenance of normal gastro-intestinal function was first demonstrated by Weiland (1) in 1914 and again by le Heux (2) in 1918. They showed that the isolated gut contained choline and that the activity of this gut decreased as the choline was washed out. The action of choline itself was feeble, but, when in the gut and changed to acetylcholine, it was found to exert an influence many times greater. Acetylcholine was thereupon regarded as a peristaltic hormone, and in 1921 Loewi (3) showed that there was a general relationship between acetylcholine and parasympathetic action, and that the action of the drug upon the parasympathetic nervous system was stimulative. During this time a number of choline esters have been synthesized—all apparently having a stimulative action upon the para-sympathetic nervous system. Among them is acetyl-beta-methylcholine (mecholyl).2 This drug has been studied by a number of workers, most of them noting that their results in general were uniform and similar. The effect of mecholyl upon the gastro-intestinal tract has, of course, been investigated (4) (5). It is the purpose of this paper to add to this present literature a study on the effect of this drug and its nullification by atropine on the colon of man. Method In the course of a study by one of us (Schube) of the gastro-intestinal tract in cases having abnormal mental states, it was observed that in the well-delineated cases of dementia praecox there was frequently a decrease in the tonus and the motility of the colon which resulted in a delayed emptying time. It was felt that this type of colon was the most suitable upon which to observe the effects of mecholyl. General Controls.—To control the study, a group of 48 cases of dementia praecox was used. These were selected at random from the available hospital population, the only criteria being the specificity of diagnosis. Specific Controls.—Each case of dementia praecox selected for the mecholyl study was used as a control on itself and on the entire mecholyl group. Each individual used in the study received a cleansing enema and two hours later a barium enema. This latter was followed under the fluoroscope and the barium allowed to run in until the colon was filled. In the control studies the tonus and motility, as well as the rate of emptying of the colon, were followed on successive days under the fluoroscope to complete emptying. In the 12 cases receiving mecholyl, this drug was administered after the colon had been filled with barium. The action of the drug was then followed by fluoroscopy and by x-ray films at approximately 5-, 10-, 20-minute, 1- and 24-hour intervals. In the five cases receiving mecholyl and atropine the action of the mecholyl was followed at 5-, 10-, and 20-minute intervals; the atropine was then administered and followed at 5-, 10-, and 20-minute and 24-hour intervals.