Abstract
The effects of comnercially available thrombin preparation on the complement system have been shown to be due to an activated form of C1 present as a contaminant. Activation of C3 and conversion of β1C to β1a in serum by thrombin preparations resulted in the generation of inflamnatory products and appeared to be initiated by the well known action of activated C1. Purified thrombin with high fibrinogen-converting activity was found to be devoid of activity in the complement system.