The protection against apoptosis provided by growth factors in several cell lines is due to stimulation of the phosphatidylinositol-3-OH kinase (PI(3)K) pathway, which results in activation of protein kinase B, (PKB; also known as c-Akt and Rac) and phosphorylation and sequestration to protein 14-3-3 of the pro-apoptotic Bcl-2-family member BAD^,,,,. A modest increase in intracellular Ca²⁺ concentration also promotes survival of some cultured neurons, through a pathway that requires calmodulin but is independent of PI(3)K and the MAP kinases,. Here we report that Ca²⁺/calmodulin-dependent protein kinase kinase (CaM-KK) activates PKB directly, resulting in phosphorylation of BAD on serine residue 136 and the interaction of BAD with protein 14-3-3. Serum withdrawal induced a three- to fourfold increase in cell death of NG108 neuroblastoma cells, and this apoptosis was largely blocked by increasing the intracellular Ca²⁺ concentration with NMDA (N-methyl-D-aspartate) or KCl or by transfection with constitutively active CaM-KK. The effect of NMDA on cell survival was blocked by transfection with dominant-negative forms of CaM-KK or PKB. These results identify a Ca²⁺-triggered signalling cascade in which CaM-KK activates PKB, which in turn phosphorylates BAD and protects cells from apoptosis.