Stress is known to affect symptoms of irritable bowel syndrome (IBS) probably by an alteration of visceral sensitivity. We studied the impact of maximal tolerable rectal distensions on cortisol levels in patients with IBS, chronic constipation and controls, and evaluated the effect of the experimental situation per se. In twenty-four IBS patients, eight patients with chronic constipation and 15 controls salivary cortisol was measured before and after repetitive maximal tolerable rectal balloon distensions and at similar times in their usual environment. Rectal sensitivity thresholds were determined. IBS patients but not controls and constipation patients had higher cortisol levels both before and after the experiment compared with similar times on an ordinary day in their usual environment (P = 0.0034 and 0.0002). There was no difference in salivary cortisol level before compared with after rectal distensions. The IBS patients had significantly lower thresholds for first sensation, urge and maximal tolerable distension than controls (P = 0.0247, 0.0001 and <0.0001) and for urge and maximal tolerable distension than patients with constipation (P = 0.006 and 0.013). IBS patients may be more sensitive to expectancy stress than controls and patients with constipation according to salivary cortisol. Rectal distensions were not associated with a further significant increase in cortisol levels.