This lecture will enable you to 1. describe why fever happens and how it differs from hyperthermia, and why it starts as a beneficial process that is best left untreated initially; 2. discuss with a vet when, why and how they manage the adverse effects of fever whilst understanding that vets do not always agree in every case; 3. describe a logical approach to therapeutic trials and their place in the investigation of fever; 4. suggest a diagnostic approach to prolonged pyrexia when asked about this in clinics.