SB 203580 is a specific inhibitor of a MAP kinase, which can inhibit reactivating kinase (RK) with IC50 of 0.6 uM. SB 203580 suppresses the activation of MAPKAP kinase-2 and prevents the phosphorylation of heat shock protein (HSP) 27 in response to interleukin-1, cellular stresses and bacterial endotoxin in vivo.