ABSTRACTBackgroundIntestinal gas is thought to be the cause abdominal discomfort in infants. Little is known about the type and amount of gas produced by the infant's colonic microflora and whether diet influences gas formation.MethodsFresh stool specimens were collected from 10 breast‐fed infants, 5 infants fed a soy‐based formula, and 3 infants fed a milk‐based formula at approximately 1, 2, and 3 months of age. Feces were incubated anaerobically for 4 hours at 37°C followed by quantitation of hydrogen (H 2 ), methane (CH 4 ), carbon dioxide (CO 2 ), hydrogen sulfide (H 2 S), methanethiol (CH 3 SH), and dimethyl sulfide (CH 3 SCH 3 ) in the head‐space.ResultsH 2 was produced in greater amounts by breast‐fed infants than by infants in either formula group, presumably the consequence of incomplete absorption of breast milk oligosaccharides. CH 4 was produced in greater amounts by infants fed soy formula than by infants on other diets. CO 2 was produced in similar amounts by infants in all feeding groups. Production of CH 3 SH was conspicuously low by feces of breast‐fed infants and production of H 2 S was high by soy‐formula–fed infants. CH 3 SCH 3 was not detected. Only modest changes with age were observed and there was no relation between gas production and stool consistency, although stools were more likely to be malodorous when concentrations of H 2 S and/or CH 3 SH were high.ConclusionsGas release by infant feces is strongly influenced by an infant's diet. Of particular interest are differences in production of the highly toxic sulfur gases, H 2 S and CH 3 SH, because of the role that these gases may play in certain intestinal disorders of infants.