Azelastine is a new oral antiasthma agent with bronchodilating and antiallergic properties. This 12-wk study compared azelastine (2, 4, 6, and 8 mg) and placebo given twice a day in asthmatics 12 to 60 yr of age requiring daily bronchodilator therapy. Patients were allowed albuterol aerosol, short-acting theophylline, and pseudoephedrine only as needed. The study was completed by 221 asthmatic subjects. No significant differences in symptoms, medication, or pulmonary function existed between groups at baseline. Analysis of the zero hour FEV1 before azelastine administration on eight occasions during the 12 wk of therapy indicated an increasing slope for azelastine 6 mg that was statistically different from that of placebo; similarly, the slope for azelastine 4 mg showed the same trend, but it did not reach statistical significance. All azelastine groups had significant reductions of as-needed medication after 1 wk; only in the 4-mg and 6-mg groups was this reduction sustained for 12 wk. Asthma symptom scores and peak expiratory flow measurements remained stable in the azelastine groups despite significant reductions in concomitant medication administration. Side effects were minor and included: altered taste (30.1 to 51.9%), drowsiness (6.0 to 16.9%), and dry mouth (3.8 to 6.1%). The occurrence of these adverse events decreased with time throughout the study.(ABSTRACT TRUNCATED AT 250 WORDS)