During hyperthermia-induced thermal panting, there was a progressive development of alkalosis, hypocapnia, hypocalcemia and plasma lactate accumulation in both mature and immature domestic fowl. 2. The results of this study further demonstrate that hypocalcemia is a general consequence of respiratory alkalosis in animals. 3. The significant (P less than 0.05) regression analysis of plasma lactate vs arterial blood pH, suggest a relationship between these two variables. 4. Plasma lactate accumulation may therefore play an important role as an extrarenal buffering component in the normal defense against severe alkalosis.