This guidance document is part of the OECD effort to provide guidance for assessing the hazards of chemical substances while gaining efficiencies and improving animal welfare. The approach described in this guidance document is to consider closely related chemicals as a group, or category, rather than as individual chemicals. In the category approach, not every chemical needs to be tested for every endpoint. Rather, the overall data for that category must prove adequate to support a hazard assessment. The overall data set must allow the estimation of the hazard for the untested endpoints.