The detection of an intact ester of testosterone in plasma is leading towards unequivocal proof of the administration of exogenous testosterone. In the current study, a sensitive screening method for the detection of nine testosterone esters in human plasma was developed. By preparing oxime derivatives of intact testosterone esters, the sensitivity of the assay was increased. Furthermore, the method included liquid-liquid extraction (LLE) as sample clean-up, as well as online separation of the target analytes from the derivatization solution. The analysis was performed by liquid chromatography (LC) coupled to tandem mass spectrometry (MS/MS). The method developed herein is simple and rapid, and was validated according to World Anti-Doping Agency (WADA) guidelines.