Adult, conscious rats have been exposed to CO-induced hypoxia for 30 min in normoxia, ambient hypoxia (FI(O(2))=14%), or hyperoxia (FI(O(2))=40%). From arterial blood gas analyses, FICO was adjusted in all experimental conditions to obtain final arterial oxygen saturations (Sa(O(2))) of approximately 60%. Oxygen uptake (V(O(2))), ventilation (V) and colonic temperature (Tc) were measured in experiments carried out at an ambient temperature of either 25 or 15 degrees C. It was found that CO hypoxia induced marked reductions in the hemoglobin O(2) half saturation pressure (P(50)). Furthermore, isolated reductions in Sa(O(2)) (with Pa(O(2)) constant) induced decreases in V(O(2)) and Tc and increases in ventilation which, as compared with normoxia, were enhanced in ambient hypoxia and reduced but still significant in hyperoxia. As suggested by previous studies, the interactions between Sa(O(2)) and Pa(O(2)) which operate on the control of metabolism and ventilation originate probably in the central nervous system.