Clonidine is classified as a class 3 performance-enhancing agent by the Asso-ciation of Racing Commissioners International and thus has the potential to in-fluence the outcome of a race. In this study, the authors developed and validat-ed a sensitive gas chromatograph and mass spectrometer method to determinethe pharmacokinetic parameters of clonidine in equine plasma samples after IVadministration of a single dose (0.025 mg/kg) of clonidine in horses. At thisdose, clonidine produced rapid and profound sedation, which could be quicklyreversed with yohimbine. Clonidine was able to produce an analgesic effect butfailed to provide maximal analgesia in all horses; the limited analgesic effectpersisted for about 60 minutes