SummaryThe Physiology of chioride ion and its relationship to clinical disorders in small animall practice is reviewed. Chioride is the major anion in the extracellular fluid and is important in the metabolic regulation of acid‐base balance. A new clinical approach is used to assess chloride ion changes after accounting for changes in free water. Using this approach chloride disorders can be divided into corrected and artifactual. Changes in free water are solely responsible for the chioride ion changes in artifactual disorders, whereas in corrected chloride disorders, chloride ion itself changes. Corrected hypochioremia is associated with increases in the strong ion differece (SID) and metabolic alkalosis and is caused by administration of solution containing a high concentration of sodium relative to chioride (e.g., Sodium bicarbonate) or the excessive loss chioride relative to sodium (e.g., vomiting of stomach contents). Administration of chioride is correction of hypochioremic metabolic alkalosis. Corrected hyperchioremia is associated with a decreased SID and metabolic acidosis and is usually the result of excessive loss of sodium relative to chloride (e.g., diarrhea), chioride retention (e.g., renal tubular acidosis), or therapy with solutions containing a high concentration of chioride relative to sodium (e.g.,0.9% sodium chloride;3–24% hypertonic saline). Treatment with sodium bicarbonate should be attempted in patients with corrected hyperchioremia and a plasma pH beiow