Investigation describing a disease state in physiochemical terms. To test the hypothesis that the hypothyroid (low-energy) person must respond differently from the normal person to physiologic stress, body compositional studies were performed on 19 randomly selected mongrel dogs (including euthyroid and hypothyroid cases). Using the multiple-isotope dilution technique, studies were performed both before and after the infusion of a hypertonic sodium bicarbonate solution. It is suggested that the significant increase in transfer of water to the extracellular space in hypothyroid dogs might be due to altered metabolic pumps, presence of abnormal mucopolysaccharide in the extracellular space, or possibly altered chemical activity of water across cell boundaries. The results of the investigation invite further study in the formulation of a specific chemical thermodynamic model of the hypothyroid state. 12 pp. Ref.