A simple quantitative assay was developed for measuring total fecal carbohydrate (CHO) excretion using stools obtained during balance studies performed for fecal fat determination. This spectrophotometric method utilizes Dreywood's anthrone reagent which reacts with equal weights of CHO whether monosaccharide or polysaccharide. Analysis of known dietary CHO solutions yielded > 90% of the known theoretical concentration. Recovery of CHO (Polycose) added to fresh stool was > 95%, inter-assay coefficient of variation (CV) 6.2%. Stool specimens stored frozen and analyzed over a 21-month period yielded stable results. Fecal CHO excretion/ day determined in 32 normal patients, ages 1 month to 13 years, on diets with varying CHO sources, ranged from 0.04 to 0.85 g, average 0.33 g, sd ± 0.24. Three patients with diseases known to be associated with CHO malabsorption studied showed markedly increased total fecal CHO excretion, up to 53% of their CHO intake. Quantitative fecal CHO excretion in these patients allowed for assessment of the severity of their disease and provided a means for evaluating the use of different dietary CHO sources in their management.