The plasmatic rate of Ca, Na and K are nearly constant during the deep lethargy of hedgehogs, common dormice and garden dormice and little differ from those measured in the active animals at 22 degrees C. Only the kaliemies of the hibernating common dormice and garden dormice are very low. The evolution of the three parameters during the alternance lethargy and periodic arousal has been analysed in terms of the metabolic and endocrinian changes which occur at those moments.