Fructose malabsorption has not been well-defined in Thai populations but there has been increasing consumption of fructose-fortified drinks.To assess the incidence of fructose malabsorption and intolerance in Thai normal subjects as well as the facilitating effect of glucose on fructose absorption.Twenty-five gram of fructose was ingested by 77 subjects (37 men, 40 women; mean age 26 and 31 y, range 20-50 y and 21-50 y for men and women, respectively). Measurement of breath-H(2) levels after fructose ingestion in each subject up to 2 h was performed. Those who showed fructose malabsorption were later given 25 g of each glucose and fructose and second tests of breath-H(2) tests were done.Fructose malabsorption was found in eleven females with a significant rise in average breath-H(2) level at 30, 60, 90, and 120 min (p< 0.001), whereas none of the males had an abnormal breath-H(2) test. Only 1 of the 11 females with increased breath H(2) had gastrointestinal symptoms. In all the fructose malabsorbers, excess breath-H(2) reverted to normal when the fructose solution was mixed and administered with 25 g glucose (p< 0.001).The incidence rate of fructose malabsorption was 11 of 77 subjects but these were female. One of the 11 had gastrointestinal symptoms. It was found that an equal amount of glucose would abolish fructose malabsorption.