Hemorrhagic colitis is a rare but well-recognized complication with ampicillin or penicillin derivative treatment. Early colonoscopy has been advocated in establishing the diagnosis by demonstrating the characteristic pattern of only right-sided involvement and so distinguishing it from other colitides. We report a patient who developed colitis after amoxycillin therapy in whom 111Indium leucocyte scan demonstrated right-sided colitis which alerted us to the diagnosis. Discontinuation of the antibiotic resulting in rapid improvement, and return of the 111Indium leucocyte scan to normal in this patient suggests that ampicillin-associated colitis should not be considered purely as a hemorrhagic disease but may in some cases have an inflammatory component.