Inflammation is a local immune response to ’foreign’ molecules, infection and injury. Leukotriene B-4, a potent chemotactic agent that initiates, coordinates, sustains and amplifies the inflammatory response, is shown to be an activating ligand for the transcription factor PPAR alpha. Because PPAR alpha regulates the oxidative degradation of fatty acids and their derivatives, like this lipid mediator, a feedback mechanism is proposed that controls the duration of an inflammatory response and the clearance of leukotriene B-4 in the liver. Thus PPAR alpha offers a new route to the development of anti- or pro-inflammatory reagents.