Summary. 2,3-Diphosphoglycerate (2,3-DPG) and adenosine triphosphate (ATP) were studied in 12 patients with shock. Observations in the first 6 hr revealed a mean value of 2,3-DPG higher than normal with a range above and below the normal limits. After this period the mean value was lower. In the presence of metabolic acidosis, the values were low. In two patients, the improvement in clinical state was associated with a rise in the level of these compounds. The mean value for ATP was slightly higher than normal in the first 6 hr and remained the same later; there was no correlation with 2,3-DPG or with pH. Our data failed to reveal any definite relation between shock and 2,3-DPG levels in the red cells. The metabolite varied independently of ATP and did not correlate with red cell age. There was a significant correlation of the levels of 2,3-DPG with the hydrogen ion concentration of arterial blood.