Azelastine is a chemically novel multifunctional antiallergy investigational drug capable of inhibiting mast-cell activation and the synthesis and/or release of chemical mediators of the upper and lower airway inflammatory response. In previous controlled clinical trials, azelastine was shown to be effective in treating the symptoms of both seasonal allergic rhinitis and perennial allergic rhinitis. The objective of this 8-week double-blind trial was to evaluate further azelastine's efficacy and safety in improving the symptoms of perennial allergic rhinitis over a prolonged period of treatment. One hundred ninety-nine patients with symptomatic perennial allergic rhinitis were randomized to receive in a double-blind fashion azelastine, 2 mg bid, clemastine fumarate, 1.34 mg bid, or placebo bid for 8 weeks. Patients treated with azelastine had superior mean percent improvements in the total symptom complex score (nose blows, sneezes, stuffy nose, runny nose, itchy nose, and itchy eyes/ears/throat) versus placebo at each evaluation point and overall across all 8 weeks (P < .01) of the trial. Improvements in the individual symptoms of rhinitis were statistically significant (P < or = .04) for nose blows, sneezes, runny nose, itchy nose, and itchy eyes, ears, and throat. Treatment with azelastine also resulted in a clinically meaningful improvement in nasal congestion. Improvement in congestion was accompanied by a decreased requirement for backup decongestant medication. The adverse experiences were generally mild and well tolerated. Azelastine provided effective prolonged relief of the symptoms of perennial allergic rhinitis with no adverse effects that would limit its long-term use.