In a four-centre prospective double-blind trial, 108 patients with ulcerative colitis in remission were randomized to receive balsalazide in doses of 3 g or 6 g/day for 12 months. The patients were assessed at 3-monthly intervals clinically, sigmoidoscopically and with routine haematology and biochemistry. Remission rates of 77% (3 g/day) and 68% (6 g/day) at 12 months were not significantly different. Intolerance reactions leading to withdrawal from the study occurred in only 9 patients (8%), all occurring in the first 7 weeks of the study. Balsalazide is therefore both highly effective in maintaining remission in ulcerative colitis and well tolerated in both conventional and high dosage (the latter equivalent to 5.5 g/day of sulphasalazine). In this study no distinct advantage in maintenance of remission has been found for the higher dose of balsalazide.