1. Amount of glutathione (GSH) in the interscapular brown adipose tissue (IBAT) of cold-adapted (5±1 °C), and 1, 3 and 7 days re-adapted (22±1 °C) rats were examined. 2. The higher amount of GSH was found in the IBAT of cold-adapted rats compared to control animals (22±1 °C). 3. After 1 and 7 days of re-adaptation, the level of GSH was still significantly higher compared to control group. 4. On the third day of re-adaptation, the quantity of GSH in the tissue was significantly lower compared to the cold-adapted group. 5. In cold-adapted animals, intensity of apoptosis in IBAT was lower, whereas in re-adapted animals (3rd and 7th day) it was higher than in control group. 6. This study indicates that GSH depletion is associated with an enhanced apoptosis in IBAT during re-adaptation.