The overall aim of this project is to characterize mechanisms underlying platelet involvement in human disease and to evaluate the therapeutic usefulness of agents that influence platelet function. During the coming year studies are proposed in three related areas: 1) continuation of platelet, fibrinogen and plasminogen kinetic studies in groups of patients with complex disorders of hemostasis-thrombosis; 2) continued in vivo evaluation of antithrombotic therapy in the baboon model of arterial thromboembolism; 3) correlative characterization of platelet size measurements in relation to platelet concentration, function, production, and mass in selected groups of patients and primate model.