The aim of this document is to provide guidance on the validation of computerised systems, compliant with Good Laboratory Practice (GLP). It specifies more precisely the procedures to follow in carrying out validations of computerised systems. It intends to help test facilities promote a common standard. However, the test facility management may use different approaches, as long as they are in compliance with the Organisation for Economic Co‐operation and Development (OECD) Principles of GLP 1. The extent of a validation may vary depending on the complexity of the computerised system. In any case the validation should demonstrate that the computerised system is suitable for its intended purpose. The Arbeitsgruppe Informations‐Technologie (AGIT) is a working group consisting of representatives from Swiss industry and Swiss GLP monitoring authorities with the aim of proposing procedures that are practical for use in test facilities fulfilling GLP regulatory requirements. These guidelines have been adapted to current practices and replace those issued in June 2000. Copyright © 2008 John Wiley & Sons, Ltd.