To evaluate some of the pathologic roles of prostaglandins (PGs) in bronchial asthma, plasma PGs levels in bronchial asthmatic patients were measured by the 9-anthryldiazomethane-HPLC method. Plasma TXB2 levels from stable bronchial asthmatic patients were higher than those from healthy subjects. Plasma PGF2 alpha levels were more elevated in atopic patients than in non-atopic ones. Plasma PGF2 alpha levels were more elevated in patients who suffered from attacks than in those who did not and plasma 6-keto PGF1 alpha levels were lower in patients who suffered from attacks than in those who did not. There was no significant difference in plasma TXB2 and PGs levels between mild and moderate asthmatic subjects. In the patients with mild attacks, aminophylline injection showed no significant effect on plasma TXB2 and PGs levels before and after the injection. These results suggest some of the roles of PGs in the pathogenesis of bronchial asthma.