The study shows that in rats acclimated to 4°C for 15 days the following parameters related to gram wet liver significantly changed in respect to control rats (24°C). The respiration rates of isolated hepatocytes without added substrates, or with hexanoate, or hexanoate + lactate, or hexanoate + oligomycin as substrates increased (+75, +73, +55, and +44%, respectively). Similarly, an increase in mitochondrial mass (+44%), as well as in state 3 oxidative rates in isolated mitochondria using glutamate, or pyruvate +malate, or palmitoyl carnitine + malate, or succinate as substrates (+200, +112, +109, and +33%, respectively), was observed. Moreover, our results show that Na pumping activity significantly increased in hepatocytes from cold acclimated rats. Since total liver mass increased in cold acclimated rats, all the above increments gained greater importance. These findings clarify the importance of the liver in the metabolic adjustments in the cold acclimated state.