An accurate and reliable method for the separation of flunixin from, and measurement in, equine inflammatory exudate and plasma by high performance liquid chromatography has been developed. Flunixin can be detected in concentrations as low as 0.05 μg/ml using an ultraviolet spectrophotometric detector at 285 nm. Samples were acidified with 2M hydrochloric acid and extracted with dichloromethane. The extract was evaporated and reconstituted in acetonitrile. Iminodibenzyl was used as Internal standard. The mean recovery of flunixin from plasma was 97.6±3.9 per cent. Particular advantages of the method are the short analysis time and ease of sample preparation. Data were obtained on the distribution of flunixin between plasma and acute inflammatory exudate following administration of a single intravenous dose of 1.1 mg/kg body weight flunixin meglumine. The drug was cleared more slowly from exudate than from plasma.