Abstract: Field and laboratory studies of thermal relations, metabolism and winter dormancy were conducted on the sand lizard, Acanthodactylus boskianus. During daily activity times the lizards were slightly, but significantly warmer than their environment. The standard metabolic rate was exponentially related to temperature. The maximum Q10 (3.86) occurred between 25 and 30°C and minimum one (1.56) between 35 and 40°C. There was no evidence of dormancy or reduced metabolism due to reduced temperature (to 15°C) in summer. Oxygen consumption was essentially the same in the field lizards and in captive ones held either in outdoor cages or at 15°C in summer, when measured at 15°C or 35°C, but consumption was significantly higher in both groups than in field animals when measured at 25°C. Lizards become dormant when exposed continuously to short photoperiods in winter. This lizard could not be maintained in an active condition through winter under laboratory conditions used successfully to keep other local lizards active. Despite the length of photoperiods used (8 h/day or 16 h/day), both groups showed a significantly reduced metabolic rate at 15°C comparable to those measured at 25°C or above. Therefore, dormancy and metabolic rate are controlled independently. The winter dormancy is controlled by reduced photoperiod, but lower metabolic rate is controlled by reduced temperature.