This is a report of one phase of an iron metabolism study of four normal college women carried out over several successive menstrual cycles. Since the larger proportion of iron exists in the body in the red blood cells, this study of necessity included determinations of hemoglobin and red cell values of the blood of the subjects. In view of the conflicting nature of the data available in the literature, daily determinations of hemoglobin and red cell content were made during the greater part of the study in the hope of making some contribution to this field of investigation. The results of these daily determinations are herewith presented and considered in relation to the different phases of the menstrual cycle. LITERATURE The literature on this subject is not extensive and the observations reported are confusing and contradictory. The one point of agreement appears to be that variations in both hemoglobin