The authors set out to critically review the current data on the efficacy of oral 5-aminosalicylic acid (5-ASA) agents for active ulcerative colitis (UC). Thirty-one studies were identified; 19 met entry criteria. Three trials with mesalamine showed statistical significance versus placebo; those with olsalazine or balsalazide did not. No agent was statistically different from sulfasalazine. In 2 of 3 trials of balsalazide versus mesalamine, results for defined primary and secondary endpoints failed to demonstrate statistically significant differences. Studies suggest that mesalamine is superior to placebo for treating active UC. Five-ASA products appear to be as effective as sulfasalazine, but available data do not suggest a difference in efficacy between any of the 5-ASA preparations.