This article describes the work that is currently being carried out by the Technical Sub-Working Group of ISO/TC23/SC19/WG3 on the definition of an extended standard for advanced transponders. This extended standard will be a logical continuation of the existing International Standardization Organization (ISO) 1996a, 11784 and 1996b, ISO 11785, an International Standard on Radio Frequency Identification of Animals (RFID) transponders. A number of transponder types and authentication methods which will be included in the extended standard are discussed, together with the solutions for the communication protocols which will be needed. (C) 1999 Elsevier Science B.V. All rights reserved.