Microglia (MG) shows a spontaneous high motility of its extensions. Upon local CNS injury processes of the surrounding microglia turn to the lesion to phagocytose degenerating axons and MG cells migrate towards the injured site. We used 2-photon laser-scanning microscopy to study the survival of MG reactions under anoxic conditions in the spinal cord of double-transgenic mice (CX3CR1-EGFP/Thy1-EYFP). Spontaneous MG activity and the MG responsiveness to laser-evoked local injury were investigated first in vivo (fully anaesthetised mice) and then post mortem (p.m.), i.e. after cardiac and respiratory arrest in the progressively degrading nervous tissue. In parallel experiments oxygen concentration was continuously measured with an oxygen sensor in the superficial layer of the spinal cord after penetration of the dura. During the 1st hour p.m. spontaneous MG activity and early MG reaction to injury remained almost unchanged, even if the partial pressure of oxygen fell from about 50 hPa in vivo down to zero within 35 min p.m.. 2-3 hours p.m. i.e. about 1.5 to 2.5 hours after complete anoxia distinct reactions of MG to injury were persisting. 4 and partly up to 10 hours p.m. still some MG responses could be observed, but with decreasing liveliness. After 5 to 10 hours p.m. MG lost its responsiveness, but some spontaneous activity could remain for about 1 hour. The observations demonstrate that MG may not only survive, but also show active reactions during long lasting anoxia and, thus, is obviously able to fulfil its function even in dead nervous tissue. Since the long lasting MG activity also persisted if the spinal cord was covered with glucose-free ACSF a particular kind of energy acquisition of MG under such a situation has to be assumed.