A selective, potent, cell-permeable inhibitor of p38 MAP kinases, inhibiting p38α (SAPK2A, MAPK14) and p38β (SAPK2B, MAPK11) with IC50 values of 50 and 100 nM, respectively; at 10 μM, has negligible effects on a range of other kinases, including other MAP kinases (ERKs, JNKs).