Beclomethasone dipropionate aerosol (BDA), 50 mug four times daily sprayed into each nostril, was compared with placebo in a double-blind crossover trial in 26 patients with perennial rhinitis. Patients received BDA for 3 weeks and placebo for 3 weeks; the order of administration was randomized. Response was assessed with daily symptom score cards and twice weekly measurements of nasal airway inspiratory resistance at a standard flow rate of 0.4 L/sec. Symptom score and nasal resistance during BDA treatment were significantly lower than those duirng placebo treatment (p less than 0.02 and p less than 0.05, respectively) in the third week. Eighteen of the patients expressed a preference for BDA, 6 for placebo, and 2 for neither (p less than 0.05). Acceptable symptomatic improvement (moderate or marked) was achieved by 54%. Mild side effects were noted by 5 patients; these included nasal irritation and bleeding in 2, aerosol-induced sneezing in 2, and headache in 1. These side effects occurred in 3 patients who used BDA, 1 who used placebo, and 1 who used both. After a 6-mo follow-up period, in which the dose of BDA was adjusted and concurrent initial oral prednisone was administered to patients who were treatment failures, 73% of the patients obtained moderate or marked symptomatic improvement. No further side effects were noted during this time. Results in those in whom a possible allergic component could be identified were not different from those of the whole group. We conclude that BDA is a useful addition to the therapy of perennial rhinitis.