Sodium bicarbonate has been thought to be effective for hypoxic lactic acidosis, but recently its adverse reactions have been pointed out. Therefore, the effects of NaHCO3 therapy in hypoxic lactic acidosis were evaluated in the anesthetized dog. Studies were carried out in four groups of adult mongrel dogs. The first group received control ventilation with hypoxic gas (5%O2 + 95%N2) and NaHCO3 therapy to adjust blood base excess. The second group did not receive NaHCO3 therapy after control ventilation with hypoxic gas. The third group breathed hypoxic gas spontaneously and received NaHCO3 therapy. The fourth group did not receive NaHCO3 therapy during spontaneous breathing of hypoxic gas. The changes of acid-base balance, CO2 and lactate of arterial blood and cerebrospinal fluid (CSF) were analysed in each dog. The conclusions were as follows; 1. The NaHCO3 therapy is not necessary for hypoxic lactic acidosis under proper ventilation, if arterial blood pH does not fall extremely. 2. The CSF acid-base balance is kept within normal ranges, so that the NaHCO3 therapy is not necessary from this point of view.