Evidence has recently accumulated showing that anti-idiotypic antibodies specific to anti-FVIII antibodies are present in the plasma of healthy individuals and of haemophilia A patients with or without inhibitors, where they can neutralise the FVIII inhibitory activity. Additionally, patients successfully desensitised towards FVIII have an increased production of anti-idiotypic antibodies with no significant reduction in anti-FVIII antibodies. We review here possible strategies for modulating the anti-FVIII immune response by idiotypic interactions.