Protein kinases drive the cellular signal transduction networks that underlie the regulation of growth, survival and differentiation. To repair the deregulations of signaling cascades that are associated with numerous disease states, therapeutic strategies, based on controlling aberrant protein kinase activity, are emerging. To develop such therapies it is crucial to have knowledge of the full complexity of signaling networks at a molecular level in order to understand the information flow through signaling cascades and their cell and tissue specificity. Antibody-based proteomic approaches (such as reverse-phase protein microarrays) are a powerful tool for using to obtain those signaling maps, through the study of phosphorylation states of pathway components using antibodies that specifically recognize the phosphorylated form of kinase substrates.