Rapeseed meal, the residue after oil extraction, is an animal feed of great commercial interest. Some genetic strains of rapeseed yield a meal which when fed in high concentration produces hemorrhagic lesions in the liver of chickens. These lesions are reduced in incidence by the simultaneous feeding of menadione. This hepatotoxicity is accompanied by elevated levels of cytochrome P-450, delta-aminolevulinic acid synthetase, and the clotting factors V and X. The hemorrhagic lesions were associated with hepatic necrosis, and menadione was protective by mechanisms other than its effect on blood coagulation.