In the rostropontine curarized Rabbit the effects of asphyxia (arresting the artificial ventilation) and of hypoxia (breathing O₂ 8% in N₂ 92%) on the unit activity of the lateral geniculate nucleus and on the EEG of the visual cortex have been investigated. Confirming the data of the literature, asphyxia induces electrical silence in a short time. Hypoxia, on the contrary, brings the activity in a stationary state characterized by a continuous firing of short bursts of spikes in the lateral geniculate, while the EEG activity shows only minor changes. This state may last as long as the hypoxia is maintained, up to 15 min in this research. Recovery, even respiring Oxygen, may require long time and be incomplete. A pattern of activity similar to that induced by hypoxia can be found occasionally during respiration with air. In this case hypoxia is no more apparently effective and the picture can be modified only by asphyxia which brings about electrical silence us usual. It is concluded with the working hypothesis that hypoxia may induce a change in the metabolism of the brain stabilizing it on a new level from which it can be displaced only by large disturbances, as total anoxia, or less predictably, by breathing air and oxygen.