Activation of lipoprotein lipase (LPL) in brown fat of the Djungarian hamster ensures substrate supply for nonshivering thermogenesis. Cold acclimation [5 degrees C ambient temperature (Ta)] in long photoperiod [light-dark (LD) 16:8] increased brown fat LPL activity from 4.7 to 22.7 nmol oleate.mg-1.min-1 within 1 day. Slight reduction of this high LPL activity was observed during prolonged cold exposure for up to 4 wk. Deacclimation (transfer from 5 to 23 degrees C Ta) caused total inactivation of brown fat LPL within 4 days. Short photoperiod (LD 8:16) also stimulates brown fat LPL activity. Its effect can be summarized by three different observations. At thermoneutrality short photoperiod elevated LPL activity to 7.1 instead of 4.7 nmol.mg-1.min-1 observed in long photoperiod. Second, at low ambient temperature short photoperiod reinforces the effect of cold acclimation. Maximum LPL activity of cold-exposed Djungarian hamsters averaged 23.7 nmol.mg-1.min-1 in long photoperiod and was elevated to 35.5 nmol.mg-1.min-1 in short photoperiod. Third, inactivation of LPL during deacclimation was delayed in short photoperiod. These results demonstrate that photoperiod as well as ambient temperature may be cooperatively used as environmental cues for seasonal acclimation of brown fat substrate supply for nonshivering thermogenesis.