This document presents guidance for conducting the Syrian Hamster Embryo Cells Transformation Assay (SHE CTA). The purpose of this Guidance document is to allow the regulatory community to use the described method as part of a weight of evidence approach in the testing of substances for carcinogenic potential. There are a number of issues which have impeded consensus on the approval of the Test Guideline; these issues mainly include the subjective nature of evaluating transformed phenotypic morphology, the limited understanding of causal molecular mechanisms leading to the transformed SHE colonies, the relatively small number of bona fide non-genotoxic carcinogens, as compared to genotoxic carcinogens, that have been tested in the SHE cell transformation assay, and the way the assay might be used in a regulatory framework.