Water exchange, temperature tolerance and oxygen consumption of the snail, Trigonephrus sp., from the southern Namib desert of Namibia were examined and related to activity. At 25°C and 15% R.H. mean water loss and food and water uptake were 5.95 mg. day−1 and 630 mg.day−1, respectively. Body temperature tracked sand temperature. Snails tolerated sand temperatures as high as 45°C. Mean ° S.D. oxygen consumption rates were 32.0 ° 2.94 μlO2.g total body mass−1.h−1 at 15°C, when the snails were active, and 11.27 μlO2.g total body mass−1.h−1 at 25°C, when the snails were inactive. These values are 2-6 times lower than those recorded for the similarly sized mesic snail, Helix aspersa. Activity experiments indicated that low ambient temperatures and high humidities were favoured by the snails. This, together with the burying behaviour of these snails during high temperatures, suggests that they limit stress by restricting activity to physiologically-favourable periods, even though more-extreme conditions may be tolerated.