Mizolastine is a new, nonsedating antihistamine providing satisfactory symptom relief in allergic rhinitis and urticaria. The purpose of this study was to use the wheal and flare skin reactions model to assess the maintenance of the pharmacodynamic effect of mizolastine, administered for 2 months. This double-blind, parallel-group study involved 60 atopic patients randomly allocated, after a 1-week placebo run-in, to once-daily 10 mg mizolastine (n = 29) or placebo (n = 31) groups. Treatment continued for 8 weeks. Prick tests were performed in duplicate with histamine chlorhydrate (10 mg/ml), codeine phosphate (9%), and five increasing concentrations (1-500 reactivity index/ml) of standardized allergen extracts (grass pollen or mites) at days 0, 7, 28, 42, and 56. After 7 days of treatment, inhibition of histamine-induced wheal was -76% and +20%, respectively, with mizolastine and placebo (P = 0.0001), in comparison with baseline; inhibition of flare was -86% and +5%, respectively, with mizolastine and placebo (P = 0.0001). Suppression was maintained to a similar extent throughout the study. Results were consistent between histamine-, codeine-, and allergen-induced tests. Safety was satisfactory in both groups. The study confirms mizolastine as a potent antihistamine which does not induce subsensitivity when taken for 8 weeks, and which can be safely recommended in allergic conditions.