OBJECTIVE: Irritable bowel syndrome (IBS) is a common functional disorder for which there is no reliable medical treatment. The aim of this study was to determine the efficacy of two herbal remedies used in the treatment of IBS. MATERIAL AND METHODS: In a randomized, double-blind, placebo-controlled trial, IBS patients were randomly assigned to one of three treatment groups: 1) Curcuma xanthorriza 60 mg daily (curcuma group) (n=24), 2) Fumaria officinalis 1500 mg daily (fumitory group) (n=24) and 3) placebo (n=58). The study treatment was applied three times a day for 18 weeks. The main outcome parameters were changes in global patient ratings of IBS-related pain and distension on a visual analogue scale (0-50 mm) between baseline and at the end of treatment. Additional outcome parameters included global assessments of changes in IBS symptoms and psychosocial stress caused by IBS. RESULTS: A total of 106 patients (mean age 48+/-12 years, 63% F) were included in the intention-to-treat group. IBS-related pain decreased by -0.9+/-11.5 (mm+/-SD) in the fumitory group, -0.3+/-9.9 in the placebo group and increased by 2.0+/-9.5 in the curcuma group (p=0.81). IBS-related distension decreased by -1.4+/-12.5 in the curcuma group, -2.1+/-9.2 in the placebo group and increased by 0.3+/-9.3 in the fumitory group (p=0.48). Additionally, the global assessment of changes in IBS symptoms and psychological stress due to IBS did not differ significantly among the three treatment groups. CONCLUSIONS: Neither fumitory nor curcuma showed any therapeutic benefit over placebo in patients with IBS. Therefore, the use of these herbs for the treatment of IBS cannot be recommended.