BACKGROUND: Andrographis paniculata is an herbal mixture used to treat inflammatory diseases. An extract of the herb, HMPL-004, inhibits TNF-alpha and IL-1beta, and prevents colitis in animal models. AIM: To determine the efficacy and safety of HMPL-004 in patients with mild-to-moderate ulcerative colitis. METHODS: A randomised, double-blind, multicentre, 8-week parallel group study was conducted using HMPL-004 1200 mg/day compared with 4500 mg/day of slow release mesalazine (mesalamine) granules in patients with mild-to-moderately active ulcerative colitis. Disease activity was assessed at baseline and every 2 weeks for clinical response, and at baseline and 8 weeks by colonoscopy. RESULTS: One hundred and twenty patients at five centres in China were randomised and dosed. Clinical remission and response were seen in 21% and 76% of HMPL-004-treated patients, and 16% and 82% of mesalazine-treated patients. By colonoscopy, remission and response were seen in 28% and 74% of HMPL-004-treated patients and 24% and 71% of mesalazine-treated patients, respectively. There was no significant difference between the two treatment groups. CONCLUSION: HMPL-004 may be an efficacious alternative to mesalazine in ulcerative colitis.