A crucial problem in the clinical treatment of many pathological states is determining the acid-base status of the patient from a sample of his blood. This study derives such a correlation from experimental data. Since the acid-base reactions of man and dog are similar, experimental data were obtained on 54 dogs subjected to various combinations of stresses corresponding to mixed respiratory and metabolic disorders. The data were introduced into the RAND computer model of fluid balance and electrolyte distribution in the human body. A nomogram was obtained for use in estimating whole-body base excess from the pH and pC02 of arterial blood samples. (See also RM-6203.) 39 pp. Ref.