Detailed morphometric studies performed in heart tissue from Swiss mice and Wistar rats show that, in comparison with other edible oils, long-term feeding of the new rapeseed oils, poor in erucic acid, do not significantly affect the incidence of myocardial background lesions, in contrast to high-erucic-acid rapeseed oil. The strong predisposition of the Sprague-Dawley rat, however, to develop myocardial necrosis is re-emphasized. The factors underlying this particularity need further clarification. The data presented and the available evidence from experiments involving pigs, monkeys and poultry show that a reduction of the content of erucic acid in rapeseed lipids, as has been achieved by selective plant breeding, considerably improves the nutritional status of the cruciferous oils.