A traditional Chinese remedy, Qing-Fei-Tang (Seihai-to, T90), has been used for treatment of chronic respiratory diseases with long-lasting cough and sputum, e.g. chronic bronchitis. We examined the effect of T90 and its main component flavonoid, baicalein, on the lucigenin-dependent chemiluminescence (CL) and leukotriene B4 (LTB4) synthesis of human alveolar macrophages (AM). AM were obtained by bronchoalveolar lavage from patients with various respiratory diseases, including sarcoidosis, idiopathic pulmonary fibrosis, bronchial asthma, chronic bronchitis and lung cancer. CL were observed by stimulating 1 x 10(5) AM with phorbol myristate acetate in the presence of lucigenin. LTB4 were generated by incubating 1 x 10(6)/ml AM with Ca ionophore A23187 for 30 min and determined by reverse phase high performance liquid chromatography and radioimmunoassay. T90 (0.2-2.0 mg/ml) and baicalein (0.1-100 microM) inhibited both CL and LTB4 production of AM in a dose-dependent fashion. These inhibitory effects were not due to cytotoxic effects of the procedure because neither 2 mg/ml T90 nor 100 M baicalein affected the viability of AM nor lactate dehydrogenase release from AM. These results suggest that T90 exerts its effect on inflammatory lung diseases through the anti-inflammatory action, i.e. inhibiting the oxidative and arachidonate metabolism of local inflammatory lung cells.