Blood gases and acid-base balance were measured in a group of patients in status asthmaticus. Simple or combined metabolic acidosis was found in 37.9% of the patients. In 25 of these, lactic acid (LA), pyruvic acid (PA) and LA/PA were increased. Increased glycolysis and anaerobic respiratory muscle glycolysis during extreme airways obstruction may be instrumental in these changes. Base deficit, not accounted for by organic acid increase, may be dependent on previously present hypocapnic hyperventilation. Possibly hyperlactemia provoked by hyperventilation may be exaggerated in severe asthma.