Many physicians order serum “electrolyte panels” or “profiles” that include sodium potassium, chloride, and bicarbonate (“CO2”; when “CO2” is included in a multitest electrolyte panel using serum, bicarbonate comprises most of what is being measured). In my experience, chloride and “CO2” are not cost effective as routine assays on electrolyte panels. If there is some necessity for serum chloride assay, as for calculation of the anion gap, it can be ordered when the need arises. Assay of serum bicarbonate is likewise questionable as a routine test. In most patients with abnormal serum bicarbonate values, there is acidosis or alkalosis that is evident or suspected from other clinical or laboratory findings (e.g., as severe emphysema or renal failure). In patients with acid-base problems, blood gas measurement or PCO2 measurement is more sensitive and informative than serum bicarbonate assay.