SYNOPSISWe used transmission electron microscopy to investigate selected aspects of the platelet response (surface activation as well as aggregation) and quantify cytoplasmic organelles within the cytoplasm of platelets obtained from both healthy control women and women diagnosed as having either common or classic migraine. Comparisons between controls and migraineurs showed no differences for: (1) the number of circulating platelets, (2) degree of surface activation, (3) amount of aggregate formation or (4) percent of hyperactive platelet populations. In contrast, platelets of migraine sufferers uniformly containeda significantly greater number of dense bodies compared to control platelets. Although we did not find functional abnormalities for the platelets obtained from migraineurs, we did demonstrate that they were altered structurally.