The present nanofiltration method is applicable on solutions of plasma-derived and recombinantly produced MBL. The MBL containing solution is subjected to a pre-treatment prior to the nanofiltration step. The nanofiltration is used for removal of viruses in general and other infectious agents to obtain an MBL product free from infectious viruses and agents. The nanofiltered MBL product is ready for preparing a pharmaceutical composition for therapeutic or prophylactic treatment of infections and other diseases in individuals with MBL deficiency and insufficiency.
