Azathioprine (AZA) is widely used for the treatment of inflammatory bowel disease. Bone marrow suppression is a common side effect with AZA treatment. However, data from AZA trials has indicated that a leukocyte count less than 5,000/mm3 was a good predictor of induction and maintenance of remission. Moreover, there is evidence that eradication of sensitized leukocytes by leukapheresis or bone marrow transplantation improves inflammatory bowel disease. We report a case of a patient who had a chronic relapse of ulcerative colitis requiring the frequent use of systemic steroids, but presented prolonged remission following AZA-induced severe pancytopenia. Also colonoscopy showed accelerated healing of diffuse active ulcers following just recovery from pancytopenia. (Intest Res 2008;6:85-89)