The efficacy of low doses of flunixin meglumine in reducing eicosanoid generation and clinical signs in response to experimentally induced endotoxaemia was investigated. Thromboxane H2 and 6-keto-prostaglandin F were measured in serum and plasma by radioimmunoassay. Plasma flunixin concentrations were determined by high performance liquid chromatography and pharmacokinetic parameters derived non-compartmentally. In horses administered flunixin meglumine before endotoxin challenge, a significant suppression in plasma thromboxane B2 and 6-keto-prostaglandin F generation was observed. Elevations in blood lactate were significantly suppressed in horses pre-treated with 0.25 mg/kg bodyweight flunixin meglumine. Reduction of the clinical signs of endotoxaemia by flunixin meglumine was dose dependent. Low doses of flunixin inhibited eicosanoid production without masking all of the physical manifestations of endotoxaemia necessary for accurate clinical evaluation of the horse's status.