We investigated the respiratory metabolism of the overwintering lizard Lacerta vivipara while in either supercooled or frozen states. With a variable pressure and volume microrespirometer and a chromatograph, we show that the oxygen consumption of the supercooled animals showed a nonlinear relationship with temperature and an aerobic metabolism demand between 0.5 and 1.5°C. A significant increase in the respiratory quotient (RQ) values indicated an increasing contribution by the anaerobic pathways with decreasing temperature. In the frozen state, two phases are easily detectable and are probably linked to the ice formation within the body. During the first 5-6 h, the animals showed an oxygen consumption of 3.52 ± 0.28 µl · g¹ · h¹ and a RQ value of 0.52 ± 0.09. In contrast, after ice equilibrium, oxygen consumption decreased sharply (0.55 ± 0.09 µl · g¹ · h¹) and the RQ values increased (2.49 ± 0.65). The present study confirms the fact that supercooled invertebrates and vertebrates respond differently to subzero temperatures, in terms of aerobic metabolism, and it shows that aerobic metabolism persists under freezing conditions.