A method for preparing a concentrated, immunoglobulin composition for treating subjects vaccinated against or infected with a pathogenic microorganism, comprising: (a) selecting a population of individuals previously vaccinated against one or more antigens associated with the pathogenic microorganism; (b) determining the level of specific antibodies immunoreactive with the pathogenic microorganism in a blood or blood component of the individuals to identify very high titre individuals having a very high titre of the specific antibodies; (c) combining blood or blood components comprising immunoglobulins from the very high titre individuals; and (d) purifying and/or concentrating the product of step (c), thereby obtaining a concentrated immunoglobulin composition. Also disclosed is a concentrated immunoglobulin composition comprising specific antibodies immunoreactive with a pathogenic microorganism, characterized in that the titre of specific antibodies of the composition is at least 5 times higher than the average titre of specific antibodies of a population of individuals previously vaccinated against one or more antigens associated with the pathogenic microorganism. The composition has a relatively high protein concentration and a low percentage of protein aggregates, and is therefore suitable for both iv and im administration. In a preferred embodiment, the pathogenic microorganism is smallpox virus or vaccinia virus.