Femoral arterial blood had been analyzed for pCO₂ and pH by Astrup technique in 10 comatose patients with respiratory insufficiency due to acute drug intoxication, all of whom eventually recovered. It was found that blood gas analysis did not always surpass clinical judgement as to the efficiency of mechanical ventilation. The readers are reminded of the difference between in vitro and in vivo CO₂ titration curves of human blood in acute respiratory acidosis.