We shall illustrate that management of patients with an acid-base disorder could be improved if the acid-base analysis was based on a better understanding of basic concepts of physiology. Three concepts of acid-base physiology and their clinical implications are emphasized in a patient with diabetic ketoacidosis. First, when an acid is produced from neutral precursors in the body, there is a net increase in the number of hydrogen ions (H<sup>+</sup>) and new anions. The corollary is that H<sup>+</sup> will be removed when the accompanying anion is metabolized to a neutral end-product or is excreted in the urine with H<sup>+</sup> or ammonium (NH<sub>4</sub><sup>+</sup>). Second, buffering of H<sup>+</sup> is beneficial if H<sup>+</sup> are removed by bicarbonate rather than being able to bind to proteins. This latter function depends on having a low tissue PCO<sub>2</sub>, due to a combination of hyperventilation plus an adequate blood flow rate to vital organs. Third, the kidneys add new bicarbonate to the body when NH<sub>4</sub><sup>+</sup> is excreted with chloride ions.