Abstract 1. 1. Ventilation, arterial blood gases and pH were measured at body temperatures (Tb) of 15, 25 and 35°C in unanesthetized black racer snakes ( Coluber constrictor). 2. 2. Arterial pH and bicarbonate concentration varied inversely with Tb, whereas ventilation, arterial P co 2 , and P o 2 varied directly with Tb. 3. 3. The slope of the pH-Tb relationship (−0.007 pH/°C) was not sufficient to maintain arterial relative alkalinity constant. 4. 4. We conclude that some factor other than the maintenance of a constant arterial relative alkalinity determines ventilation as Tb changes in this species.