International Standards are the ‘gold standard’ against which regional, national and international laboratories and manufacturers calibrate their own working standards. They are calibrated in units of biological activity which are assigned following extensive studies involving multiple international laboratories. They are not designed to be used as a working reference standard in laboratory bioassays. To support the intended use of the International Standard for Interleukin-1β, we advise the customers to use Non-WHO Reference Material for Interleukin-1β (86/552).