This Guidance Document has been prepared to provide the pathologist reading slides from endocrine and reproductive studies (eg the updated TG407 and longer studies) with sufficient information to be able to identify the often subtle histopathologic changes that are associated with endocrine disruption in target tissues. The histopathology guidance was initially developed to assist pathologists involved in Test Guideline 407 studies. The guidance focuses on areas that were inconsistently reported during validation studies ie male and female reproductive tissues, pituitary gland and mammary glands. It aims to provide a consistent approach to terminology and grading and advice on morphological changes associated with endocrine disruption pathways. After positive feedback from these groups it was proposed that the guidance could be used for other reproductive/endocrine studies in addition to the TG407.