Previous studies have revealed morphologic platelet abnormalities, particularly inclusions, in patients who have acute malarial infections. To determine the possible role of aspirin (ASA) in the etiology of these abnormalities, the thrombocytes of 14 normal men were examined before and after ingestion of 2 Gm. of ASA. A significant decrease in platelet size was noticed after ASA; however, no ultrastructural alteration of these circulating platelets was found, although functional impairment was manifested in vivo (bleeding time) and in vitro (aggregation). It is concluded that inclusions and other morphologic abnormalities in thrombocytes of malaria patients are not caused by aspirin ingestion.