NIBSC performs testing on diphtheria vaccine and antitoxin products to ensure compliance with requirements for potency and safety. Traditional potency assays involve challenging animals with toxin to confirm protection after immunisation with vaccine. NIBSC led the European validation studies to replace these traditional challenge methods with an in vitro antibody assays for potency testing of diphtheria component in combined vaccines.  A range of the methods for safety and potency developed at NIBSC are now included in the Ph Eur and introduced for testing of combined vaccine used in the UK childhood immunization programme. In vitro antigen content and degree of adsorption assays have also been developed for improved characterisation of diphtheria toxoids and for monitoring batch to batch consistency.