The chapter commences with blood gases, indications, sampling, blood gas symbols, Normal values of arterial blood gases etc. In detail are given along with pathological reasons and normal values of PCO2, SO2, O2, PO2, TCO2, CO2, Blood pH, Base excess/deficit etc. Next the chapter covers – automation in ABG analysis. Subsequent chapter space is taken by Electrolyte analysis by flame photometer and by ISE automated methods. Various conditions where electrolyte values are high and low are also given in ample detail.