The SDH (EC 1.3.99.1) activity of both whole brain and mid-brain homogenates and the specific oxygen consumption of mid-brain homogenate are significantly lower in old than in young lizards. Short-term cold stress (1 h at 0–4°C) did not induce a significant change in the enzyme activity of the whole brain homogenate, but the activity was depressed in the mid-brain homogenate of lizards of both age groups, not showing appreciable age-dependency of the response. The respiratory rates of mid-brain homogenates of both young and old lizards were depressed following cold stress. Lizards of both age groups showed almost complete reversal of depressed respiratory rate during the same time, i.e. between 30 and 45 min of rewarming at room temperature (30 ± 2°C). Though statistically insignificant the old lizards showed a trend of slower rate of recovery as compared to the young lizards, suggesting further detailed studies on the problem in question.