Oral mesalamine (Asacol) in a dose of 3.2 g/day was administered in a 16-week placebo-controlled trial in 38 patients for the treatment of mildly to moderately active Crohn's colitis or ileocolitis. Eighteen patients continued a stable dose of prednisone of no more than 20 mg/day and 20 patients did not take prednisone. Changes in the Crohn's Disease Activity Index (CDAI) were used as the primary measure of efficacy. Oral mesalamine was effective in achieving partial or complete remission in 60% of patients as compared with 22% of placebo-treated patients. However, only 20 of 38 patients completed the 17-week study. The others withdrew early because of worsening of symptoms or were dropouts counted as failures. The high percentage of early withdrawals prevented comparison of mean 17-week CDAI scores. Although the number of patients in this study was relatively small, Asacol 3.2 g/day appears to be safe and effective treatment for mildly to moderately active Crohn's colitis and ileocolitis as compared with placebo, and this regimen is an option for treatment of patients who fail or are intolerant of sulfasalazine.