It has become clear that 5-amionosalicylic acid (5-ASA) is the therapeutically active moiety of sulphasalazine in the treatment of inflammatory bowel disease (IBD). Orally ingested conventional release 5-ASA tables demonstrate that the drug is rapidly and completely absorbed from the upper gastrointestinal tract. However, the drug is poorly absorbed from the colon, where it is considered to act from the luminal side. 5-ASA is subsequently acetylated, mainly in the gut wall, to the thereqeutically inert metabolite, N-acetyl-5-aminosalicylic acid (Ac-5-ASA). To improve clinical efficacy, a wide range of 5-ASA delivery systems have been developed.