Our randomised study in parallel groups, double-blind double placebo, has compared the efficacy, onset of action and safety of terfenadine and cetirizine in chronic idiopathic urticaria. Over a fourteen day period, patients of the first group received a tablet containing 120 mg of terfenadine, those of the second group a tablet containing 10 mg of cetirizine. Symptoms were assessed every two hour period for the ten first hours on the first day (D1), and before and at the end of the study by the investigators. 193 patients were included by 48 dermatologists between May 1989 and July 1990. Both groups were well matched for all general characteristics and baseline symptoms scores. The onset and the intensity of regression of symptoms (pruritus, erythema and discomfort during sleeping time) were similar in both treatment groups public physicians: improvement of pruritus in over 90% of the patients. Meanwhile the tolerability was good or excellent for dermatologists and allergologists for 92% of the patients under terfenadine against 81% of the patients under cetirizine (p < 0.05). Adverse events (fatigue and drowsiness) were significantly reported less frequently (p < 0.05) in patients on terfenadine (19%) than on cetirizine (33%). This study confirms the efficacy of terfenadine compared with cetirizine in the treatment of chronic idiopathic urticaria. Adverse events were less significant for terfenadine (n = 18) than for cetirizine (n = 29) (p < 0.05).