p38 mitogen-activated protein kinase (MAPK) is a member of the stress activated kinase family with a molecular weight of 38 kD. MAPK can be activated by a number of stimuli including heat, changes in osmolarity, irradiation, and cold. The MAPKs require dual phosphorylation (threonine and tyrosine) for enzymatic activation. The p38 MAP kinase is required for G2 cell cycle delay after UV irradiation, also participates in cytokine production (IL-6 and erythropoietin). The Poly6224 antibody recognizes human, mouse, and rat p38 MAPK and has been shown to be useful for Western blotting.