There is discrepancy in the literature concerning the effect of the menstrual cycle on bowel function and pain syndromes such at irritable bowel syndrome. In addition, recent studies indicate a difference in the CNS processing of rectal stimulation in normal subjects and patients with IBS. This study will determine the differences in the perception of rectal balloon distention in the follicular and luteal phases of the menstrual cycle, in control subjects with no bowel symptoms and volunteers with IBS, and will compare the CNS processing of this signal using functional MRI , again in the two phases of the menstrual cycle.