Metabolic acid-base disturbances are frequently encountered in the emergency department, and many of these patients are critically ill. In the evaluation of patients with these maladies, it is important for the emergency clinician to determine the cause, which can usually be elicited from a thorough history and physical examination. There are several mnemonics that can be used to form an appropriate list of potential causes. Most of the time, the management of these patients requires no specific treatment of the acid-base status but, rather, requires treatment of the underlying disorder that is causing the acid-base disturbance.