The epsilon4 allele of apolipoprotein E (apoE) is a genetic risk factor for Alzheimer's disease. Studies also suggest that the epsilon4 allele may be a risk factor for poor outcome following head trauma, brain haemorrhage and ischaemia. The mechanism by which the presence of an apoE epsilon4 allele and certain brain injuries act to predispose to Alzheimer's disease and poor outcome following brain injury is unknown. We questioned whether poor outcome after brain injury was due to direct modification by apoE protein and its gene variants of susceptibility to glutamate-mediated excitotoxic injury and apoptosis, mechanisms of cell death which occur following ischaemia and trauma. We investigated the effect of the presence or absence of endogenous murine apoE protein and different apoE isoforms in modification of the survival of murine embryonic cortical neurons exposed to the glutamate agonist, N-methyl-D-aspartic acid (NMDA) or apoptotic insult by staurosporine, and on the amount of brain injury sustained following a hypoxic-ischaemic insult in vivo to the brain of neonatal mice transgenically expressing human apoE epsilon3 or epsilon4. Our data provide evidence that apoE does not appear to alter neuronal viability following diverse types of acute neuronal insult, e.g. hypoxic-ischaemic or acute exposure to injurious agents in the models we have examined. This suggests that if apoE does modify the extent of brain damage and recovery after injury, it seems unlikely to be a result of direct or indirect modulation of excitotoxic or apoptotic cell death.