Hyperestrogenemia has been implicated in the pathophysiology of myocardial infarction. Because marked augmentation of the titer of Hageman factor is brought about by the administration of estrogens in humans and by prolactin or estrogen infusion in hypophysectomized rats, we measured the plasma concentrations of estradiol, prolactin, and clotting factors participating in surface-mediated reactions of coagulation in survivors of myocardial infarction. We observed higher titers of Hageman factor, prolactin, and high molecular weight kininogen but no significant change in estradiol or prekallikrein in survivors of myocardial infarction compared with controls. The titer of Hageman factor tended to be directly associated with the prolactin titer. We also report an increase in factor VII activity and spontaneous shortening of prothrombin time in the cold-stored plasma of survivors of myocardial infarction. In such individuals as well as in the control group, the titer of Hageman factor appeared to be responsible for half of the observed increase in factor VII activity and two thirds of the observed shortening of prothrombin time. These data indicate that although the titer of Hageman factor strongly influences the cold activation of factor VII, other factors may affect these phenomena.