For coagulation studies on rat blood requiring consecutive samples it is best to obtain blood from the tail, under ether anesthesia, by amputation of one vertebra for each sample wanted. Higher activity levels of clotting factors in unanesthetized rats are not due to stress. The coagulation activation phenomenon is always present in capillary blood samples from unanesthetized rats and is enhanced in serial blood samples unless three vertebrae are amputated to obtain the sample. The procedure described here, applied to unanesthetized rats, could serve as a model for the testing of antithrombotic drugs.