5-Aminosalicylic acid (5-ASA) compounds occasionally exacerbate diarrh
oea in patients with inflammatory bowel disease. This is thought to be
due to a secretory mechanism in most cases. A patient with presumed i
ntolerance to sulphasalazine and 5-ASA preparations who developed endo
scopic and histological evidence of disease relapse after a rectal cha
llenge with mesalazine is reported.