Growth hormones are proteins produced by the anterior pituitary gland responsible for bone and tissue growth through their effects on carbohydrates, lipids and proteins metabolisms. Despite strict regulations banning the use of recombinant equine growth hormone, this substance is suspected to be misused to improve the horse physical performances. In order to check whether the regulation is fulfilled or not, controls are organized and a new analytical screening tool potentially able to detect such abuse was investigated in this paper. An untargeted metabolomics approach, based on liquid chromatography coupled to high resolution mass spectrometry, was developed and applied to characterize and compare horse urinary and plasmatic metabolic profiles upon reGH administrations. After minimal sample preparation, biological fluids were analyzed by LC-ESI(+/-)-Q-TOF. Data processing was performed by XCMS software and multivariate data analysis applied to the generated data set allowed building OPLS models to discriminate control versus treated populations. Results demonstrated significant metabolic modifications consecutively to the reGH treatment. A comparative study between urinary and plasmatic signatures was performed to evaluate the resulting metabolomic models and to asses their respective interests in the scope of real application for screening reGH administration.