Abstract 1. 1. The acid base metabolism was investigated in a temperate zone bird, the rock partridge, exposed to ambient temperatures of 20–45°C and relative humidity < 30%. 2. 2. Mean normal values at ambients of 20–30°C were as follows: Arterial pH7.54 units; Pa co2 26.6 mmHg; [HCO − 3]22.6 mM/1; BE—0.5 m-equiv/l. 3. 3. The intensive hyperventilation at ambients of 42 and 45°C was accompanied by slight respiratory alkalosis i.e. Pa co2 of 25.0 mmHg and arterial pH of 7.561 and 7.585 respectively. 4. 4. The possible existence of efficient mechanism for regulating Pa co2 level is discussed.