Mature male rats fed rapeseed oil for 16 weeks had a higher incidence of cardiac lesions than did control rats fed a mixture of lard and corn oil. Both high-erucic and low-erucic rapeseed oils were associated with cardiac necrosis and fibrosis. A dose response in the incidence of such lesions was obtained after 16 weeks of feeding various levels of Span oil (B. campestris, 2.7-percent erucic acid), but with Oro oil (B. napus, 0.6-percent erucic acid) an increased incidence of lesions occurred only at the top levels. Zephyr oil (B. napus, 0.3–0.7-percent erucic acid) and a ‘deodorizer condensate’ diluted in olive oil were also associated with a high incidence of cardiac lesions. The refining of oil appeared not to change its nutritional properties, but partial hydrogenation of Zephyr oil decreased the cardiopathogenic e