1. The distribution of glycogen and nonglycogen structures in megakaryocytes as demonstrated by the Hotchkiss technic is described.

2. A semiquantitative method for estimating the relative amounts of megakaryocyte glycogen in a bone marrow aspiration has been developed and is described. The result is expressed as the Megakaryocyte Glycogen Score (MGS).

3. The megakaryocyte glycogen scores on 25 aspirations from 14, healthy, young adult volunteers are presented and fall between 20 and 80, except in those subjects with recent acute blood loss or repeated phlebotomies over a period of years.

4. Subjects who have had repeated phlebotomies tend to have higher MGS than subjects without repeated phlebotomies. These higher values of MGS exist in the absence of abnormalities in the reticulocyte count, bone marrow differential count, platelet count, hemoglobin, hematocrit, wbc and differential, and rbc.

5. In one subject with a normal MGS, a 500 cc. phlebotomy was followed in one hour by a decrease in MGS. The MGS had increased above normal by four hours postphlebotomy and was still elevated 25 days after phlebotomy.

6. Implications of these observations are discussed.

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