Studies of the acid-base equilibrium of the plasma in pregnancy have been incomplete either because they were based on too few patients or because all of the various cations (sodium, potassium, calcium, magnesium or total base) and anions (Cl-, HCO3-, HPO4-, SO4-, protein and organic acid) were not determined. Stander and his co-workers made a complete study of the acid-base equilibrium in three pregnant women. Oard and Peters made a similar study in twelve pregnant women, but omitted determinations of SO4- and organic acid. Numerous other reports of studies of the carbon dioxide content and, in a few instances, ofph have been published, but the number of reports of total base in pregnancy is extremely small. However, similar reports on nonpregnant persons are also few and are based on a study of a relatively small number of subjects. In table 1 are listed some