Different prevalence and degree of nonspecific bronchial hyperreactivity between seasonal and perennial rhinitis. From the patients observed at our respiratory allergology service, we selected patients with rhinitis only, without any past or present respiratory symptoms, for our study. All these patients had normal pulmonary function, were administered carbachol or methacholine bronchial challenges, and had one or more skin reactions to perennial or seasonal allergens. Patients were allocated to three groups: group A, patients with seasonal rhinitis who were administered nonspecific challenges out of season; group B, patients with seasonal rhinitis tested during the season; and group C, patients with perennial rhinitis. The three groups were divided into subgroups according to the duration in years of rhinitis and to the degree of nonspecific bronchial responsiveness. The distribution into four groups of reactivity, arbitrarily defined as normal and mildly, moderately, and severely increased reactivity, was as follows: group A, 124, 21, 30, 22; group B, 75, 15, 7, and 21: and group C, 69, 17, 39, and 72, respectively. The patients of group C (perennial rhinitis) demonstrated a distribution significantly (p less than 0.001) different from subjects with seasonal rhinitis, both group A and group B. Our results are consistent with the hypothesis that perennial rhinitis is much more important than seasonal rhinitis as a risk factor for developing nonspecific bronchial hyperresponsiveness. 