[3H]leucine incorporation into 16 electrophoretic protein fractions from the neocortex and the hippocampus and their relative content have been estimated in various physiological states of ground squirrels: in torpor, in 3 transition phases, in long-term wakefulness and a fortnight after forced arousal in winter. The changes are greater in the neocortex than in the hippocampus. Incorporation is not the same in naturally awake animals and forced awake animals.