A gramma-globulin aqueous solution can be subjected to sterile heat-treatment without losing its activity when the treatment is conducted in the presence of at least one stabilizer which is a monosaccharide, disaccharide or sugaralcohol added to the solution. The stabilizer serves to decrease the harmful polymer or anticomplement activity of the gamma-globulin before the treatment but to maintain the titer of a wide variety of antibodies to various viruses and bacteria, while the infectivity of viruses possibly contained is completely removed.
An additional stabilizer, which is a neutral amino, a neutral inorganic salt, an organic carboxylic acid salt or a surface active agent, assists the abovementioned stabilizer when used together with it.