Abstract Using etretinate as a model compound, the bone changes characteristic of hypervitaminosis A were evaluated in the rat in terms of tibial bone-breaking strain. Dose-related effects were observed in the dose range of 5–30 mg/kg p.o. for 15 days. The model proved a simple and precise means of assessing hypervitaminosis A in this species. Isotretinoin also showed a small but significant reduction in tibial breaking strain, but with a shallow dose-response curve in the range of 50–150 mg/kg.