Thrombopenic purpura is characterized by uniformity in its blood picture but presents marked variations in its severity and clinical course from acute to chronic. The study on which the present article is based comprised 153 cases observed over ten years (1926 to 1936). The following typical blood conditions were noted in this group: (1) absence of anemia, unless considerable bleeding had taken place, (2) absence of abnormalities in the leukocytic picture and (3) marked diminution in the number of platelets. In addition, the bleeding time was prolonged; clot retraction was absent and a positive capillary resistance reaction present. Symptoms of bleeding were present in all cases; these included easy bruising, spontaneous ecchymosis, purpura, epistaxis and bleeding gums. There was considerable variation, however, in the amount of bleeding, which frequently was severe at first but usually was mild in cases of more chronic disease. Bleeding was especially severe when associated with