The bedside method of determining the serum bicarbonate level described previously1 provided a simple, rapid means of obtaining information for a rough clinical appraisal of acid-base balance. The improved method, described here, preserves all the advantages of the previous method, is two to four times more accurate, and is easier to perform. In the improved method, phenol red replaces diphenylcarbazone as the pH indicator. This is advantageous for several reasons. 1. Phenol red is stable, while diphenylcarbazone is not. 2. During the titration phenol red does not develop interfering purple colors as diphenylcarbazone often does. 3. The end point is sharper with phenol red than with diphenylcarbazone. A further improvement has been made by finding simple means of limiting the main source of error in the bedside bicarbonate method—a variation in the amount of dissolved carbon dioxide remaining in the sample during titration. More thorough agitation before titration and