Individuals with impaired intestinal absorption of fructose may exhibit recurrent abdominal discomfort after the ingestion of fructose-containing foods. We report on patients with this disorder in whom the diagnosis was made by the fructose hydrogen breath test.We investigated 293 patients with recurrent abdominal pain, meteorism or diarrhea in connection with the ingestion of fruits, apple juice or soft drinks. Mixed expired air was collected before and at 30 minute intervals after a fructose load and analysed thereafter by a hydrogen sensitive electrochemical cell. Incomplete absorption of fructose was defined as a peak rise in breath hydrogen of > 20 ppm.108 out of 293 patients showed an abnormal peak rise after fructose (mean 71.8 ppm, SD 31.4). This malabsorption of fructose was associated with clinical symptoms in 79 of them. Sensitivity and specificity of the fructose hydrogen breath test were 98 or 86 per cent respectively. 19 patients with an abnormal breath test and symptoms following fructose were reexamined after a load with equimolar concentrations of glucose and fructose. Hydrogen breath test was normal in all of them, none developed abdominal discomfort.A considerable number of individuals suffer from dysfunctional gastrointestinal problems due to fructose malabsorption. The fructose hydrogen breath test is a simple, sensitive and noninvasive method for the diagnosis for this disorder. Possible means of treatment are dietary fructose restriction or a modification of the diet in which fructose-containing foods are exchanged for those with equal concentrations of glucose and fructose.