The influence on airway conductance of inhaled aerosols of prostaglandin F(2)alpha (PGF(2)alpha), histamine, and prostaglandin E(2) (PGE(2)) was studied in 10 patients with spirometrically reversible bronchial asthma and in 10 healthy subjects with no history of lung disorder. Both groups responded with bronchoconstriction after inhalation of PGF(2)alpha but the asthmatic patients were about 8,000 times more sensitive to the compound than were the healthy controls. In the patients, but not in the controls, PGF(2)alpha often caused a long-standing decrease in airway conductance with symptoms resembling allergen-provoked asthmatic attacks. On the other hand, the patients showed less than a 10-fold increase in sensitivity to histamine, and the ratio of histamine: PGF(2)alpha doses causing a 50% decrease of airway conductance was 2.6:1 and 2,400:1 in controls and patients respectively. Inhalation of PGE(2) while moderately but consistently increasing airway conductance in controls, had a variable-occasionally slight bronchoconstrictive-effect in patients. The decrease in airway conductance by a given dose of PGF(2)alpha was little modified by the simultaneous inhalation of a 100-times higher PGE(2) dose. It is suggested that endogenous, locally formed PGF(2)alpha may play an important part in the pathogenesis of bronchial asthma.