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Basking can substantially reduce thermoregulatory energy expenditure of mammals. We tested the hypothesis that the largely white winter fur of hamsters (Phodopus sungorus), originating from Asian steppes, may be related to camouflage to permit sun basking on or near snow. Winter-acclimated hamsters in our study were largely white and had a high proclivity to bask when resting and torpid. Resting hamsters reduced metabolic rate (MR) significantly (>30%) when basking at ambient temperatures (T-a) of similar to 15 and 0 degrees C. Interestingly, body temperature (T-b) also was significantly reduced from 34.7 +/- 0.6 degrees C (T-a 15 degrees C, not basking) to 30.4 +/- 2.0 degrees C (T-a 0 degrees C, basking), which resulted in an extremely low (<50% of predicted) apparent thermal conductance. Induced torpor (food withheld) during respirometry at T-a 15 degrees C occurred on 83.3 +/- 36.0% of days and the minimum torpor MR was 36% of basal MR at an average T-b of 22.0 +/- 2.6 degrees C; movement to the basking lamp occurred at T-b<20.0 degrees C. Energy expenditure for rewarming was significantly reduced (by >50%) during radiant heat-assisted rewarming; however, radiant heat per se without an endogenous contribution by animals did not strongly affect metabolism and T-b during torpor. Our data show that basking substantially modifies thermal energetics in hamsters, with a drop of resting T-b and MR not previously observed and a reduction of rewarming costs. The energy savings afforded by basking in hamsters suggest that this behaviour is of energetic significance not only for mammals living in deserts, where basking is common, but also for P. sungorus and probably other cold-climate mammals.