The effects of high ambient temperatures on blood acid base status were studied in four breeds of fowl. 2. All breeds efficiently regulated body temperature below ambient temperature at 45 degrees C (Tb = 38.521 + 0.110Ta, at 25-45 degrees C). 3. A slight hypocapnia was partly compensated for by a decreased HCO3 concentration. This resulted in only a slight respiratory alkalosis at extreme temperatures (+0.021 and +0.042 pH units at 42 and 45 degrees C, respectively). 4. Changes in Paco2 were negatively correlated with tidal volume: Paco2 (torr) = 33.10390 - 1.17493 VT(ml); r = -0.925, P much less than 0.001. 5. The present findings are consistent with an hypothesis that modulation of tidal volume during thermal panting might play a major role in acid-base regulation.
