Numb is an endocytic adaptor protein that functions in the endocytosis and intracellular trafficking of membrane receptors and adhesion molecules. Numb localization and function have been shown to be regulated by phosphorylation through atypcial protein kinase C at several key sites. Here, we use Liquid Chromatogrpahy, Tandem Mass Spectrometry to identify additional Numb phosphorylation sites not yet characterized.