Proposed mechanisms of neurodegeneration focus generally on the triggering of toxic biochemical pathways by an increased intracellular concentration of Ca2+. Recent evidence also suggests that Ca2+ causes transcriptional activation of so-called 'cell-death genes'. Efforts to elucidate the basis of selective vulnerability have relied on animal models of delayed neuronal death in the hippocampus. Biochemical and morphological data indicate that delayed neuronal death is a form of programmed cell death, or apoptosis. Observations that specific genes are activated transcriptionally for prolonged times in neuronal populations that are undergoing delayed death suggest that active gene expression is part of the neuronal-death cascade. Although a direct causal role remains to be proven, evidence implicates certain genes in neuronal-death pathways.