Authorisation of biocidal products in the European Union is a two-stage process, where the biocidal active substances are approved in a first step at the European level, and the biocidal products are authorised in a second step at member state level. If an active substance is designated as Candidate for Substitution during this process, a comparative assessment must be carried out for each biocidal product containing this active substance. The aim of the current project was to evaluate the practicability of the existing technical guidance for this procedure by conducting a number of exemplary comparative assessments, and to develop recommendations for improvements.