It is now a well recognized fact that the entire group of sulfonamide compounds can be added to those which may produce various disorders of the blood. Thus the rather high incidence of acute hemolytic anemia in patients receiving these drugs is now well established, as well as is the fact that the drugs are capable of producing acute agranulocytosis. Furthermore, in some instances they are capable of stimulating granulopoietic activity to the point of producing leukemoid reactions. This makes it all the more remarkable that very few reports have been presented indicating that these compounds are capable of affecting the blood platelets. During the past eighteen months we have had an opportunity to study 3 cases in which thrombopenic purpura presumably developed because of the administration of sulfathiazole. Reports of 2 of these are incorporated in this paper, the third being omitted because of circumstances whereby we are unable