THE lability of the blood coagulation substance, factor VIII (antihaemophilic globulin, AHG, AHF), has hindered its investigation and has thus led to a search for techniques to stabilize it. Additions of glycerol1,2, gelatine3,4, human serum4, and human serum albumin4 were all found to stabilize factor VIII activity, but the degree of effectiveness of such additions has not been denned. The investigation reported here was an attempt to evaluate the action of glycerol in quantitative terms.