20 patients with a diagnosis of chronic idiopathic urticaria were entered into a double-blind placebo-controlled cross-over study. All patients completed the trial and during the assessment period they were treated with placebo, BW 825C (4 mg) and BW 825C (8 mg) according to a fully randomised and balanced treatment plan. Both doses of BW 825C were found to be highly effective and significantly better than placebo in controlling signs and symptoms of urticaria. Few adverse reactions were reported and in this small group of patients there was no significant difference from placebo in reports of drowsiness or any other side-effects.