AbstractA commercial plasmin‐treated human immunoglobulin was studied for its antibody spectrum and anticomplementary activity. Except for a decrease in anti‐vaccinia antibody titers in two of three paired samples collected before and after plasmin treatment, there was practically no fall in titers of diphtheria antitoxin and of antibodies to measles, rubella and mumps viruses. Among the three major fractions isolated from the preparation, the plasmin‐resistant 7S IgG fraction showed the highest anticomplementary activity when tested by our routine method described in the ‘Japanese Minimum Requirements’. The Fab fraction showed moderate anticomplementary activity which was thought to be due to the selective consumption of C3. On the contrary, the Fc fraction was not found to be anticomplementary in our test method. In some of the above‐mentioned features, the preparation seems to be different from the domestic product formerly studied b