Abstract: Forth nine cases ofirritable bowelsyndrome presenting with diarrhea or constipation and 10 normalcontrols were tested by the lactulose hydrogen breath test to determine the oral cecal passage time,and bacterial overgrowth in the intestines was examined as well;the positive rates were noted.Positive cases were treated with prepulsid for 1 week ,and the pre and post treatment passage times were com pared. The passage times in both the constipation and the diarrhea types of the irritable bowel syndrome were prolonged versus controls (P< 0.05) ,butthere was no differencein the rates of bacterial overgrowth in the intestines between the two types (P>0.05).Oral cecal passage times and clinical sym ptoms were significantly improved after treatment versus pre treatment (P< 0.05).Intestinal moti lity disturbance could lead to bacterial overgrowth, which might be a pathogenic factor in the irritable bowel syndrome.The lactulose hydrogen breath test was an observation parameter to judge clinical therapeutic efficacy.

Key words: irritable bowel syndrome(IBS), intestinal bacterial overgrowth, lactulose hydrogen breath test(LHBT), oral-cecal passage time(M-ITT)