Irritable bowel syndrome (IBS) patients inWestern countries usually manifest autonomic nervedysfunctions and abnormal psychological behaviors. Thepurpose of this study was to assess whether Oriental IBS patients with predominant bowel symptomsalso exhibited similar abnormalities. We enrolled 40 IBSpatients from the outpatient clinic and 20 controls withnormal daily bowel habit for study. The IBS patients were further divided according totheir predominant bowel habit: 20 wereconstipation-predominant and 20 werediarrheapredominant. Sympathetic function was evaluatedby sympathetic skin response (SSR) while vagal cholinergic function wasdetermined by measuring R-R interval variation (RRIV) inelectrocardiography during rest and deep breathing.Psychological parameters were assessed by scales of the Minnesota Multiphasic Personality Inventory(MMPI) and the Hopkins Symptom Checklist (HSCL-90). IBSpatients, despite their bowel habit, showed normal SSRresponse. RRIV during deep breathing was significantly lower in constipation-predominant IBS patientsthan in controls or diarrhea-predominant IBS patients(16.5 ± 3.1% vs 20.5 ± 4.8% and 21.5± 4.6%, P < 0.001). IBS patients alsoexhibited abnormal MMPI measuring scores on depression, hysteria,paranoia, and masculinity/femininity scales. Inaddition, they also had more severe psychologicaldistress in the items of HSCL-90 measurement. Inconclusion, vagal dysfunction characterizes Orientalconstipation-predominant IBS patients seeking medicalhelp. Abnormal psychoneurotic profiles also exist inthese IBS patients, irrespective of their bowelhabits.