1. The non-respiratory pH, which is based upon in vivo carbon dioxide titration curves, was compared with empirical corrections to the base excess values derived from in vitro carbon dioxide titration curves.
2. These two indices were highly correlated in thirty-two measurements made at between-sample intervals of less than 12 h in four patients with acute exacerbations of chronic bronchitis and in two patients with ketoacidosis.
3. These observations confirm that the acute whole body CO2 titration curves established in anaesthetized man by others can be applied to acute clinical situations, so that either index can adequately describe these disturbances.