This method offers a simple quick technic for separate expired air samples. Both CO2 and O2 analysis may be completed within 5 minutes as compared to 15-20 minutes by Haldane. Ninety-five per cent of the duplicate CO2 analyses as determined with the Beckman C model (110-160 mm Hg range) will agree within 0.10% with duplicate Haldane data. A Beckman instrument of a narrower range and/or greater sensitivity would improve this accuracy. In our experience the Beckman C model (110-160 mm Hg range) allows better results than does the more elaborate and expensive E-2 model.