The contact phase of coagulation in the presence of heparin.

The effect of heparin on the contact phase of coagulation has been investigated by a technique utilizing a solution of toluidine blue in calcium chloride. Heparin in a concentration of 7 units/ml. of plasma does not inhibit contact activation by glass. It is suggested that heparin does not prevent the activation of factor XII (Hageman factor) by glass or the subsequent formation of active factor XI (plasma thromboplastin antecedent).