Native factor VII (F. VIIn) can be activated by thromboplastin or by the kallikrein-system. This gives rise to two different forms of activated factor VII. We thus discern Factor VIIn, cold activated factor VII (C.P.A-F. VIIa) and thromboplastin activated factor VII (T-F. VIIa).We developed one- and two-stage assays that distinguish between these forms and we tried to establish their interrelationship.T-F. VIIa could be obtained in a form devoid of lipid components and still clearly distinguishable both from factor VIIn and from C.P.A.-F. VIIa. It activates factor X in a thromboplastin-independent process, whereas C.P.A.-F. VIIa is unable to do so.The difference between F. VIIn and C.P.A.-F. VIIa is that the latter is converted into T-F. VIIa much more quickly in a process that shows less species specificity with regard to the type of thromboplastin used.No differences could be seen between T-F. VIIa obtained from V, VIIn directly or via C.P.A.-F. VIIa.