Disorders of the upper respiratory tract, particularly allergic rhinitis are commonly associated with bronchial hyperresponsiveness. The latter may be responsible for chronic cough, a common symptom in patients with allergic rhinitis, which, as previously shown, can be the sole presenting manifestation of bronchial hyperresponsiveness. Theophylline is widely used in patients with asthma for its bronchodilator effect, whereas its action on bronchial reactivity is controversial. The aim of this study was to determine the effect of theophylline administration on bronchial hyperresponsiveness in patients with allergic rhinitis complaining of chronic cough. Fourteen patients were studied. All of them were judged atopic on the basis of positive skin tests to common allergens. During control, spirometry, flow-volume curves and specific airway conductance (SGaw) were measured. Bronchial challenges were then performed with increasing concentrations of carbachol, and dose-response curves were constructed. The concentration of carbachol, which decreased SGaw by 35% from baseline (PD35) was determined by interpolating from the dose-response curve. After control measurements patients received in a randomized, double-blind crossover fashion either theophylline 10 mg/kg/day orally or placebo for 30 days. Measurements were then redone. After a washout period of 8 days the measurements were repeated, and patients received theophylline or placebo for a second period of 30 days. Measurements were again performed at the end of this last study period. During control all patients had normal baseline lung function data and showed marked bronchial hyperresponsiveness, PD35 amounting to 26 +/- 7 micrograms of carbachol (normal value greater than 160 micrograms). No significant changes in PD35 were noted after placebo and washout when compared with control values.(ABSTRACT TRUNCATED AT 250 WORDS)