Protein phosphorylation is a fundamental event in the regulation of a large number of intracellular processes. Phosphorylation of specific tyrosine residues is the result of activation or stimulation of their respective protein tyrosine kinases. The phosphorylated proteins can be auto-phosphorylated kinases or certain cellular protein substrates. Tyrosine-phosphorylated proteins are involved in signal transduction and in the regulation of cell proliferation. Antibody to phosphotyrosine provides an excellent tool for the detection, characterization, and purification of phosphotyrosine containing proteins. This MAb shows no cross-reaction with other phosphoamino acids and is superb for multiple applications including staining of formalin/paraffin tissues.