Recent studies have suggested a role for phosphatidylinositol (PI) 3-kinase in cell survival, including the survival of neurons. We used rat sympathetic neurons maintained in vitro to characterize the potential survival signals mediated by PI 3-kinase and to test whether the Akt protein kinase, a putative effector of PI 3-kinase, functions during nerve growth factor (NGF)-mediated survival. Two PI 3-kinase inhibitors, LY294002 and wortmannin, block NGF-mediated survival of sympathetic neurons. Cell death caused by LY294002 resembles death caused by NGF deprivation in that it is blocked by a caspase inhibitor or a cAMP analog and that it is accompanied by the induction of c-jun, c-fos, andcyclin D1 mRNAs. Treatment of neurons with NGF activates endogenous Akt protein kinase, and LY294002 or wortmannin blocks this activation. Expression of constitutively active Akt or PI 3-kinase in neurons efficiently prevents death after NGF withdrawal. Conversely, expression of dominant negative forms of PI 3-kinase or Akt induces apoptosis in the presence of NGF. These results demonstrate that PI 3-kinase and Akt are both necessary and sufficient for the survival of NGF-dependent sympathetic neurons.