Purpose: The purpose of this study was to determine if rectal lidocaine reduces visceral and thermal hyperalgesia in IBS patients compared to rectal placebo. Methods: In a prospective double-blind, placebo controlled, crossover design, twenty six women with IBS (mean age 30 ± 10 years) and ten control women (mean age 29 ± 7 years) rated pain intensity and unpleasantness (VAS 0–10) to barostat distension of the rectum (35 mmHg) and thermal stimulation (immersion in 47° C water) of the foot before and after rectal administration of either lidocaine jelly or saline (placebo) jelly. Rectal and thermal stimuli were repeated at 5, 10, 15, 20, 40 and 50 minutes following administration of the agent. Serum lidocaine levels were obtained in all patients at 5 and 50 minutes following rectal administration of lidocaine and saline jelly. Results: Intrarectal lidocaine (300 mg) significantly reduced pain report to rectal distension and thermal stimlulation of the foot in all of the IBS patients. The effects were greater than those of placebo (p <.001) and most pronounced effects were present within 5 to 15 minutes after the onset of treatment. In controls, rectal lidocaine did not decrease pain report to either rectal orthermal stimuli. These changes were likely due to the local effect of lidocaine rather than a systemic effect as the rectal lidocaine did not result in detectable blood levels of lidocaine. Conclusions: The results of this study support the hypothesis that local anesthetic blockade of peripheral impulse input from the rectum/colon reduces both visceral and thermal hyperalgesia in IBS patients. The results provide further evidence that visceral hyperalgesia and thermal hyperalgesia in IBS reflects central sensitization mechanisms that are dynamically maintained by tonic impulse input from the rectum/colon. Rectal administration of lidocaine jelly may also be a safe and effective means of reducing hypersensitivity in IBS patients. Supported by a Clinical Research Award from the ACG.