This protocol uses mitogen-activated protein/ERK kinase (MEK) to activate the extracellular-signal-regulated (Erk) mitogen-activated protein (MAP) kinases upon agonist binding to receptors. Protocol includes information about: Harvest, Immunoprecipitation and Kinase Reaction. Also includes following solutions: Laemmli Sample Buffer (1X), ATP Mix, Kinase Buffer (10X), Lysis Buffer. Helpful protocol hints are also included.