The volume and composition of intestinal gas of 11 normal subjects was studied by means of a technic in which an intestinal infusion of argon was used to wash out gases present in the bowel. These studies indicated that the bowel normally contains relatively small quantities of gas ranging from 30 ml to 200 ml. The composition of this gas was highly variable although N2 was usually the predominant gas whereas O2 was present in concentrations of less than 2 per cent. Gases produced within the bowel (CO2, H2 and CH4) accounted for most of the gas of three subjects. Intestinal bacteria directly influence the composition of intestinal gas through their production of H2, CH4 and CO2 and utilization of O2 and, by reducing the luminal PN2, indirectly influence the N2 content of the bowel.