THE EXTENSIVE and serious disturbances of cardiorespiratory function which result from diseases of the heart or lungs have been studied exhaustively by many investigators. 1 The consequences of these diseases include a variety of compensatory changes which mitigate to some extent the harmful or discomforting effects of the diseases themselves. Among the respiratory enzymes, hemoglobin offers an example of such a compensatory change by its increase in chronic anoxic states effected by an increase in blood volume in congestive failure and by an increase in red cell mass in severe chronic pulmonary disease. Other respiratory enzymes have not, however, been studied extensively in instances of disease. Only fragmentary observations have been made on the effect of disease on the activity in the blood of carbonic anhydrase, the enzyme which is involved in the transport of carbon dioxide. Hodgson 2 and Lambie, 3 on the basis of a small number