BACKGROUND Second-generation antihistamines, reported to lack central nervous system depressant activity, may be considered to have a clinical advantage over traditional antihistamines. OBJECTIVE To compare the effectiveness, at recommended doses, of an extended-release formulation of nonprescription brompheniramine and prescription terfenadine in the treatment of allergic rhinitis. METHODS This was a double-blind, randomized, placebo-controlled, multicenter, parallel study. Subjects with symptoms of allergic rhinitis received brompheniramine 12 mg (n = 96), terfenadine 60 mg (n = 96), or placebo (n = 95) twice daily for 14 days. Subjects returned on treatment days 3, 7, and 14; at which times, the investigator assessed symptom severity (i.e., rhinorrhea; sneezing; nasal blockage; pruritus of the eyes, nose, or pharynx; watery eyes; and postnasal drip). The investigator and the subject each completed a global efficacy evaluation, and subjects were interviewed regarding the occurrence of adverse experiences. Symptoms were analyzed as summed severity scores for (1) all symptoms and (2) for the symptom cluster of rhinorrhea, sneezing, and nasal blockage. RESULTS At all post-baseline evaluations (days 3, 7, and 14), brompheniramine was significantly better (P < or = .05) than terfenadine and placebo for both sets of summed symptom scores and for both global assessments. Terfenadine was significantly better (P < or = .05) than placebo on the physician's global at day 14. Central nervous system-related complaints were the most frequently reported adverse experiences among all three groups; somnolence was reported most frequently by brompheniramine-treated subjects. CONCLUSIONS A nonprescription, extended-release formulation of brompheniramine, 12 mg bid, provided significantly better relief of symptomatic allergic rhinitis than terfenadine, 60 mg bid.