Background: Many patients with irritable bowel syndrome (IBS) have lowered sensory thresholds to rectal distention when compared to control subjects, a phenomenon called visceral hypersensitivity. Aim: To investigate the usefulness of a rectal barostat as a diagnostic tool in IBS and if there are differences in visceral hypersensitivity in different groups of IBS patients. Patients and Methods: Ten healthy subjects and 19 IBS patients, defined using Rome II criteria (12 with constipation, three with diarrhea and four alternating between diarrhea and constipation), were studied. Sequential isobaric rectal distentions, from 2 mmHg up to a maximal pressure of 52 mmHg or when the patients reported pain, were carried out. Visceral hypersensitivity was defined as a pain threshold under 38 mmHg. Results: Only 26% of IBS patients had visceral hypersensitivity (16% and 43% of patients with IBS and constipation and IBS and diarrhea or alternating symptoms, respectively, p =NS). Pain threshold in controls, patients with IBS and constipation and patients with IBS and diarrhea or alternating symptoms was 43.8±6.6, 45.3±9.2 and 40.8±9.2 mmHg, respectively (p =NS). Conclusions: Our results do not support the usefulness of the electronic rectal barostat as a diagnostic method to diagnose IBS.