Abstract
A modification of the method of Owren & Aas for the determination of relative arbitrary substance concentration of coagulation factors (II+VII+X) in plasma is presented. The coefficient of variation on repetends (today – yesterday) is reduced to 0.03 for results in the therapeutic as well as the ‘normal’ interval. An unusual composition of the plasma may be revealed. Thromboplastin-absorbed bovine plasma should be kept at -70 °C.