Abelin JG, Patel J, Lu X, Feeney CM, Fagbami L, Creech AL, Hu R, Lam D, Davison D, Pino L, Qiao JW, Kuhn E, Officer A,Li J, Abbatiello S, Subramanian A, Sidman R, Snyder E, Carr SA, Jaffe JD. Mol Cell Proteomics, 2016. Profiling posttranslational modifications represents an alternative dimension to gene expression data in characterizing cellular processes, as genetic processes alone are not sufficient to explain the entirety of biochemical mechanisms or disease etiology. For example, some cellular phenotypes resulting from chemical perturbations are partially or entirely mediated by changes in cell signaling through protein phosphorylation. To access this dimension of cellular information, we sought to develop a common platform on which cellular phosphosignaling responses could be profiled across thousands of samples. To this end, we developed a targeted MS assay that profiles a reduced-representation set of phosphopeptides that we show to be strong indicators of cellular responses to chemical perturbagens.