We describe three methods of sample preparation for the liquid chromatography coupled with mass spectrometric measurement of insulin-like growth factor-I concentration in blood. One method involves trypsin digestion, the second involves intact protein quantification and the third method is a combination of the first two. Step-by-step directions are provided for sample collection and handling including transport, storage conditions as well as detailed instructions for preparation for analysis, which can be modified for larger or smaller sample volumes as needed. A fully 15N-labelled internal standard is used and the merits of a single-point calibrator are discussed. Example instrumental conditions are presented for both intact and digest methods.