P38 mitogen-activated protein kinases (p38 MAPK) are mitogen-activated protein kinases that respond to stress stimuli and have roles in cell differentiation, apoptosis and autophagy. There are four known p38 MAP kinases; these are named p38-α, -β, -γ, and –δ. Because of the role p38 plays in stress signaling, p38 inhibitors hold promise as therapies for inflammatory diseases such as rheumatoid arthritis and autoimmune disorders. While some inhibitors block all four p38 MAP kinases, others will only inhibit one or two of the subtypes.