, et al. Comparative trial of remission prophylaxis in quiescent Crohn's disease with oral 4-aminosalicylic acid versus 5-aminosalicylic acid slow release tablets. Can J Gastroenterol 1993;7(2):241-244. 4-Aminosalicylic acid (4-ASA) has been suggested co be effective in the treatment of active ulcerative colitis. Oral slow release tablets containing 4-ASA (1.5 g/day) were compareJ with those containing 5-ASA (l.5 g/day) in the maintenance treatment of Crohn's disease in a one-year doubleblind, randomized study involving 60 patients with ileocolonic or colonic involvement. Patients were enrolled if in stable remission without active drugs for more than two months but less than one year. Total colonoscopy anJ ileoscopy were performed at enrollment and at the end of the study. The cumulative relapse rates at 12 months were 37% in the 4-ASA and 38% in the 5-ASA group. Clinical relapse, as defined by a rise in the C rohn's disease activity index (COAi) of more than 100 points co values higher than 150, was accompanied by a statistically significant rise m serum concentrations of soluble interleukin-2 receptor and by an increased percentage of activated peripheral blood T cells. There were no statistical differences between the 4-ASA and the 5-ASA goup regarding relapse rates, the rise in COAi during relapse or the increase of soluble interleukin-2 receptor concentrations. It is concluded that 4-ASA may be as effective as 5-ASA in the maintenance treatment of quiescent Crohn's disease and that there were no differences in the severity of relapse between both treatment groups.