We have shown that pharmacological inhibition of HSP90 ATPase activity induces apoptosis of myoblasts during their differentiation. However， the signaling pathways remain not fully characterized. We report that pharmacological targeting of HSP90 with 17-AAG activates the intrinsic pathway including caspase-dependent and caspase-independent pathways. 17-AAG induces the typical apoptotic phenotypes including PARP cleavage， chromatin condensation， and nuclear fragmentation with mitochondrial release of cytochrome c， Smac/DIABLO， procaspase-9 processing， and caspase-3 activation. AIF and EndoG redistribute from the mitochondria into the cytosol and are partially translocated to the nucleus in 17-AAG-treated cells. These results suggest that caspase-dependent and caspase-independent pathways should be considered in apoptosis of myogenic cells induced by inhibition of HSP90 ATPase activity.