A mathematical model of the Base Excess curve of blood was developed and then programmed into a digital computer coupled to an automatic plotter. Values for serum albumin, globulin and mean corpuscular hemoglobin concentrations were fed to the computer and theoretical Base Excess curves were generated. Normal values gave a curve which closely approximated the experimentally derived curve of SIGGAARD-ANDERSEN. When values characterizing hypoproteinemia, hypochromia or tris-(hydroxymethyl)-aminomethane buffering were introduced, Base Excess curves were produced which varied, often markedly, from the traditional curve.