The aim of this study was to determine the long-term efficacy and safety of mizolastine, a new second-generation antihistamine with European approval, in the treatment of perennial allergic rhinoconjunctivitis. In this study, 141 patients were treated with once-daily mizolastine 10 mg or 15 mg in a 5-month open-label extension of a 1-month double-blind, placebo-controlled trial, which assessed once-daily mizolastine 10 mg. Mizolastine significantly reduced the nasal subscore (sneezing, rhinorrhoea, itch; end-baseline +/- SD, -2.5 +/- 6.3), nasal obstruction (-1.2 +/- 2.6) and rhinoscopy scores (-1.3 +/- 2.6), and improved ocular and total nasal scores after 6 months' treatment. Improvement was maintained for the duration of the study with no loss of drug efficacy. Adverse effects were mild with no specific effects associated with prolonged use. These results clearly demonstrate that mizolastine is effective and well tolerated in the long-term treatment of perennial allergic rhinoconjunctivitis. The significant clinical improvement in nasal blockade may reflect mizolastine's histamine/5-lipoxygenase dual inhibition.