Thirty-four patients with ulcerative colitis completed a double-blind assessment comparing the efficacy of two weeks of treatment with nightly retention enemas containing 3 g sulphasalazine or placebo. Symptom grading, sigmoidoscopic appearance, rectal biopsy specimens, and diary records were used to assess benefit and side effects. The active drug conferred significant benefit compared with placebo as shown by several criteria, but this benefit was confined to patients not already taking sulphasalazine by mouth. Overall assessment showed improvement in 11 of the 16 patients (70%) given the active treatment but in only two of the 18 (11%) given placebo. No side effects attributable to the drug were observed, even in patients previously intolerant to oral preparations. The logical therapeutic role of sulphasalazine enemas in ulcerative colitis would appear to be in patients who experience side effects such as nausea, abdominal discomfort, or headaches when taking the drug by mouth.