The purpose of this report is to cite a case of purpura fulminans treated successfully with heparin sodium and to make a brief interpretive comment on the fundamental pathological process in this syndrome. The clinical and laboratory data suggested that thrombosis, not hemorrhage, is a primary mechanism of the pathological physiology. The clinical syndrome variously known as purpura fulminans, purpura hemorrhagica, purpura gangrenosa, and purpura necrotica was first described by Guelliot in 1884 and later (1886) by Henoch. Since that time, more than 100 cases have been reported in which one of the above diagnoses has been made. The exact number is impossible to determine, because many clinical syndromes other than purpura fulminans are included in these reports. In retrospect, it is difficult to determine how many cases may represent meningococcemia, allergic purpura, idiopathic thrombocytopenic purpura, streptococcic and other types of bacteremia, or numerous other possible entities. The cases of