The present study was to examine whether andrographolide, a diterpenoid lactone isolated from the anti-inflammatory herbal medicine Andrographis paniculata (Burm. f.) Nees. (Acanthaceae), has the ability to prevent phorbol-12-myristate-13-acetate (PMA)-induced reactive oxygen species (ROS) production, as well as N-formyl-methionyl-leucyl-phenylalanine (fMLP)-induced adhesion by rat neutrophils. Results demonstrated that PMA (100 ng/ml) induced rapid accumulation of H2O2 and O2. in neutrophils within 30 minutes. Andrographolide (0.1 to 10 microM) pretreatment (10 min, 37 degrees C) significantly attenuated the accumulation of these two oxygen radical metabolites. Administration of andrographolide also significantly prevented fMLP-induced neutrophil adhesion. These data suggest that preventing ROS production and neutrophils adhesion may confer andrographolide the ability to be an anti-inflammatory drug.