The investigation of the coagulation activity of factor VIII in persons with different blood groups is important e.g. for a more accurate diagnosis of Willebrand's diseases. The recent study data confirm that lower values of the factor VIII activity are typical of healthy subjects with blood group 0, residing in Saint Petersburg, versus persons with blood groups A, B, and AB. Limits were defined for the permissible fluctuations of the factor VIII activity. With P = 0.95, they are estimated by formula A(n) = m +/- 1.64 omega and their approximate values are as follows: A(n) = 102 +/- 48 for persons with blood group 0, A(n) = 124 +/- 54 for persons with blood groups A, B, and AB.