To assess whether malabsorption of specific sugars is easily detected in a pediatric population by interval measurement of breath hydrogen excretion, hydrogen concentration was determined following administration of oral sucrose to six sucrose-intolerant children with congenital sucrase-isomaltase deficiency and in 16 sucrose-tolerant control subjects. Breath samples were collected by means of a newly devised nasal prong technique not requiring active patient cooperation and suitable for use in all age groups. Breath hydrogen concentrations obtained by samples collected by this method correlated highly (r = 0.94) with the previously validated modified Haldane-Priestley tube method for sampling alveolar air. Identification of sucrose-intolerant individuals was achieved on the basis of hydrogen excretion: peak values, expressed as parts per million above baseline (deltappm), equalled 114 +/- 63 (mean +/- SD) versus 2.4 +/- 3.6 deltappm in control subjects (P = 0.007). Best discrimination between the groups occurred at 90 minutes postingestion. The findings validate this simple method for collection of expired air and demonstrate that breath hydrogen determination permits the noninvasive detection of sucrose malabsorption in children.