We read with great interest the recent article by Naganuma et al.1 The authors showed a significant effect of indigo naturalis in treating patients with ulcerative colitis (UC) in a randomized, placebo-controlled trial. In their study, patients were randomly assigned to groups given a daily dose of 0.5, 1.0, or 2.0 g of indigo naturalis or placebo for 8 weeks. The proportion of patients with a clinical response at week 8 was significantly higher in the 0.5-g indigo naturalis group (69.6%; P = .0002), 1.0-g indigo naturalis group (75.0%; P = .0001), and 2.0-g indigo naturalis group (81.0%; P < .0001) than in the placebo group (13.6%).