Blood gas analysis provides valuable information about both the extracellular acid-base status and gas exchange. A blood gas analyzer measures pH, partial pressure of oxygen(pO(2)), partial pressure of carbon dioxide (pCO(2)), O(2) saturation, and hemoglobin concentration. A number of calculated parameters can be derived from these direct measurements such as bicarbonate concentration, base excess, oxygen content, etc. This contribution introduces the basic technical aspects of a blood gas analyzer and then describes some of the parameters that facilitate evaluation of the acid-base status and the oxygenation status of the blood. Finally, proper sampling and handling of blood gas samples is addressed.