Abstract In order to determine directly whether saliva has any specific thromboplastic activity or whether its effect in accelerating blood coagulation is nonspecific, we compared saliva with commercial tissue thromboplastins in the following modified hematologic tests: 1. 1. In the one-stage prothrombin-time test, the prothrombin activity curve was simulated very closely when saliva replacing tissue thromboplastin was used in the same manner. 2. 2. In the thromboplastin-generation test, saliva showed a definite thromboplastin generation over a period of time, constantly increasing and then deteriorating. Commercial tissue thromboplastin did not show any detectable generation at any time or at any concentration.