Previous studies of the circulation rate in man in various types and degrees of anemia (1, 2, 3) have concerned themselves chiefly with comparisons of circulation rates of groups of anemic individuals with the rates of normal individuals.Inasmuch as the normal rate varies greatly from one individual to another, it occurred to us that it might be of interest to study the cardiac output as well as other functions of the circulation of a given subject while in the anemic state and also at intervals during his recovery. It would thus be possible to show in that individual the adjustment to the condition of anemia; and a group of such studies might give a clearer picture of the adaptive process than could be obtained from purely statistical data on circulation rates and related functions.The present investigation is a study of the cardiac output in eight anemic subjects both during the stage of anemia and at intervals in the period of recovery. The initial oxygen capacities of the blood varied from 5.4 to 14.4 volumes per cent. Two were suffering from primary anemia, four from secondary anemia following hemorrhage from gastric or duodenal ulcer, one from secondary anemia with carcinoma of the stomach, and one had a secondary anemia associated with purpuric manifestations. When the experiments were made, the subjects were in all instances apparently well compensated to their anemia; while at rest in bed, temperature, respiratory rate and pulse rate were within normal limits except that on two occasions the pulse was as high as 90. All experiments were done in the morning, under basal conditions: that is, after at least 12 hours without food, and half an hour of complete rest in bed.