As part of the ICH process of harmonization of testing guidelines for immunotoxicity, the European Society of Toxicologic Pathology (ESTP) has contributed to the scientific discussion on methods and evaluation of immunotoxicity studies with technical and scientific recommendations on toxicologic pathology. The weighing and sampling of immune organs is discussed taking into consideration specifically the value of lymph node weighing and the selection of appropriate lymph nodes for the detection of local and systemic effects. The different techniques of bone marrow preparation are considered for routine and extended investigations. Criteria are given for the gross and histopathological detection of effects in Peyer's patches. For the histopathological evaluation it is strongly recommended that each compartment within the different lymphoid organs is investigated separately and semiquantitatively since this approach has shown to increase the sensitivity and specificity of immunohistopathology.