To the Editor: The article by Drs. Lennon and Lemann (1) published in the August issue of the ANNALS OF INTERNAL MEDICINE makes a further contribution to quantification of the compensatory adjustments that will normally resist deviations of plasma pH in acid-base disturbances of both respiratory and metabolic origin. It is nevertheless to be hoped that the authors will gain no adherents for their proposal to replace the Henderson-Hasselbalch equation in treating acid-base equilibria in blood plasma. Among the physicochemical constants characterizing an acid, along with its molecular weight, freezing point, and so forth, is to be reckoned its dissociation constant