SB 203580, a pyridinyl imidazole, has been observed to suppress p38 mediated activation of MAPKAP kinase-2 (MAPKAPK-2 or MK2), yet does not disrupt JNK activity.Mitogen-activated protein kinases (MAPK) are a group of serine and threonine-specific kinases sensitive to cellular stress, heat shock, and proinflammatory cytokines. p38 (p38 MAPK) is crucial for normal inflammatory and immune responses as it regulates the expression of varying cell surface receptors, cytokines and transcription factors. SB 203580 inhibits heat shock protein 27 (HSP 27) phosphorylation and has been shown to induce the activation of Raf-1. SB 203580 has also been shown to inhibit phosphoinositide-dependent protein kinase 1 (PKB Kinase), consequently preventing the activation of PKB/Akt. SB 203580 is a useful tool to assess the physiological roles of p38, and for deriving and maintaining embryonic stem cells. SB 203580 is an inhibitor of p38 α, p38 β, Cox-1, Cox-2, GSK, TXA Synthase and RICK.