AbstractAs the rat is the preferred species for teratogenicity studies in our laboratories, the Chernoff‐Kavlock assay was modified and validated for use in this species. The Alpk:AP (Wistar‐derived) strain, which is also used routinely for toxicology studies, was used, under standard SPF conditions. Twenty‐six chemicals have been assayed to demonstrate the utility of the system as a predictor of rat teratogens and to develop a set of rules for interpretation of the results. Routes of chemical administration were largely gavage, with some dermal, subcutaneous, inhalation, and intraperitoneal applications. The use of the assay in five modes to assist the toxicological evaluation or understanding of chemicals is displayed. These modes are (1) as a pre‐screen, (2) to compare analogues/homologues, (3) to provide a rapid hazard estimate, (4) to generate a dose‐response, and (5) to test a h