Several studies have suggested that patients with bronchial asthma are more susceptible to the potential effects of nitrogen dioxide (NO2) than healthy subjects, with respect to airway responsiveness and lung function. We investigated whether these differences are paralleled by differences in the cellular and biochemical response within the airway lumen. Twelve subjects with mild extrinsic asthma and eight normal subjects breathed either filtered air or 1 ppm NO2 in a single-blind manner during intermittent exercise for 3 h. Bronchoscopy with bronchoalveolar lavage (BAL) was performed one hour after each exposure, and on a third day without exposure (baseline day). Prostanoids, leukotrienes and histamine were analysed in BAL fluid, and the cellular composition of BAL fluid was assessed. In the asthmatic subjects, NO2 induced a small mean drop in forced expiratory volume in one second (FEV1). Differential cell counts in BAL fluid did not reveal significant effects of NO2. Levels of 6-keto-prostaglandin1 alpha (6-keto-PGF1 alpha) were decreased, and levels of thromboxane B2 (TxB2) and prostaglandin D2 (PGD2) in BAL fluid were increased after NO2 compared to filtered air exposure; whereas, prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha), histamine and leukotriene levels did not change significantly. The normal subjects showed no change in lung function parameters and a small increase in TxB2 after breathing NO2. We conclude that in subjects with mild asthma NO2 is capable of inducing an activation of cells, which is compatible with enhancement of airway inflammation, even if lung function parameters and cellular composition of BAL fluid are not markedly affected.(ABSTRACT TRUNCATED AT 250 WORDS)