The ends of eukaryotic chromosomes, known as telomeres, consist of repetitive DNA sequences, multiple proteins and noncoding RNAs. Telomeres are dynamic structures that play crucial roles as guardians of genome stability and tumor suppressors. Defects in telomere length or protein composition can accelerate aging and are seen in telomere syndromes, which affect various proliferative tissues such as the bone marrow or the lungs. One of the biggest challenges in the telomere field is to identify the molecular changes at telomeres that occur during normal development, in cancer and in telomere syndromes. To tackle this problem, our laboratory has established a quantitative telomeric chromatin isolation protocol (QTIP) for human cells, in which chromatin is cross-linked, immunopurified and analyzed by mass spectrometry. QTIP involves stable isotope labeling by amino acids in cell culture (SILAC) to compare and identify quantitative differences in telomere protein composition of cells from various states. (C) 2016 The Authors. Published by Elsevier Inc.