Anton de Groot has written the 5th edition of his book Patch Testing (ISBN/EAN 978-90-813233-6-9), now containing information on test concentrations and vehicles for 5200 chemicals. It contains the combined information of Patch testing 4th edition and the UPDATE 2018-2022.  The book will not be available commercially. However, the 4th edition can be ordered on the website www.patchtesting.info and the UPDATE can be downloaded there for free.