Parathyroid hormone (PTH), an 84-amino acid peptide hormone, is a major regulator of calcium homeostasis. Quantification of PTH in serum is used clinically to investigate calcium imbalances and for monitoring osteodystrophy in patients with renal failure. In addition to intact PTH, several PTH fragments are found in circulation. Recent studies have shown that accurate quantification of PTH fragments may provide valuable clinical information in certain scenarios. In this chapter, a high-resolution mass spectrometry–based method for quantification of PTH (1–84) and its fragments is described. This method involves immunoaffinity capture of intact PTH and PTH-fragments followed by liquid chromatography–high-resolution mass spectrometry (LC–HRMS).