The purpose of this Guidance Document (GD) is to provide pathologists, toxicologists, and associated scientists with recommended guidelines for performing the pathology tasks required by the specifications of TG 412 and 413, and for optimising the value of pathology-related tasks in these studies. This document is structured to follow the specifications in TG 412 and TG 413 and to provide recommendations and supplementary information to these specifications in the temporal sequence one would encounter in planning, participating in, and reporting the results of pathology tasks in a 28 or 90 day inhalation toxicology study utilising TG 412 and TG 413. It is also intended to conform to the recommendations provided in GD 39, Guidance Document on Acute Inhalation Testing, and to the OECD Principles of Good Laboratory Practice (GLP).