The content of blood endogenous ethanol (EE), acetaldehyde (EA), the concentration and activity of liver alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) in seasons with maximum temperature differences (summer and winter) in wild mammals: small wild rodents - voles (V; n = 50), the large aboriginal northern animals - yakut horse (YH; n = 35) and reindeer (R; n = 35) were studied. The concentrations of EE and EA in animal blood were determined by gas chromatography with mass spectrometric detection (GCMS). The contents of EA and EE in blood were increased in northern animals in the winter and were significantly higher than in all seasons of the year than in laboratory rats. The seasonal changes were obtained in the level of metabolites associated with seasonal changes of catalytic parameters and physicochemical properties of ADH and ALDH. The differences in the mechanisms of seasonal activation of liver ADH and ALDH were found in R and YH.