1. The intravenous injection of a soya bean preparation containing a trypsin inhibitor into 2 dogs and 3 rabbits produced the following effects: prolongation of the clotting time and of the prothrombin time, and increase in the antiproteolytic activity of the blood plasma or serum.
2. Identical results were obtained in one experiment in which a crystallin trypsin inhibitor from soya bean was used.
3. The significance of these results is briefly discussed.