?TO THE EDITOR.— The interesting article by Kalendovsky et al, on platelet hyperaggregability in young patients with stroke, in the January 1975 issue of the Archives (32:13, 1975) prompts me to make this report (March 1975) of results obtained from a pilot study conducted on 15 patients with stroke (mean age, 63 years) vs 15 control patients of the same age, 15 young asymptomatic persons (mean age, 25 years) and 15 other patients given anticoagulant therapy with warfarin sodium (Coumadin) (mean prothrombin time, 20.6 seconds).Time sequence of mechanical clot resistance. Values given are mean of each group. 450 200 411 Hypercoagulable Stroke Group 261 Controls of Similar Age 208 Young Controls 76 Warfarin Sodium Patients 8 10 12 18 20 22 24 26 28 30One of the coagulation tests performed was designed here. It consisted of drawing 10 ml of fresh venous blood, placing 0.5 ml in each of