Intestinal transit is an important indicator of small-bowel function. This study served to investigate oro-cecal and duodeno-cecal transit times of different carbohydrate test meals and to evaluate intra- and interindividual variability of the breath hydrogen test. Breath hydrogen was analysed by an electrochemical cell in 25 healthy volunteers. Oro-cecal transit time of lactulose was much shorter than that of a standardized normal test meal. Duodeno-cecal transit was approximately one hour shorter than oro-cecal transit. Considerable intra- and interindividual differences were observed. It is concluded that results of lactulose test meals do not permit conclusions as to the physiological situation. Large intra- and interindividual variability of transit times must be taken into account in any study using the breath hydrogen test.