To determine how factors involved in infant carbohydrate metabolism could be effectively assayed in vitro, fecal materials from healthy infants were obtained and tested with fermentation mixtures incorporating glucose, fructose, and lactose incubated under aerobic and anaerobic conditions. The amounts of organic acids, hydrogen, carbon dioxide, and methane produced were determined. Principal component analysis indicated that products of the three sugar systems produced very similar factor patterns and, therefore, all three sugars may not be required to adequately characterize intestinal microbial fermentation processes. Moreover, the fermentation processes under aerobic and anaerobic conditions produced essentially identical cluster patterns of the factors from the three sugar systems. Collectively, the results indicated that two sugar systems, glucose and lactose, measured under aerobic fermentation conditions sufficed in accounting for most of the variation among babies.