Reflned rapeseed oils with a high and a low-ehcic-acid content were fed to male Wistar rats for six months. Histomorphometric studies of the rhanges in predetermined heart sections indicated a significantly higher incidence and a greater severity of myocardial lesions in rats fed high-erucic-acid (regular) rapeseed oil than in rats fed either low-erucic-acid rapeseed oil or sunfloworseed oil. After administration of various amounts of Primor oil, a French rapeseed oil containing 0.3 % erucic acid, the observed minor changes were indistinguishable in nature, incidence and severity from those observed in control animals.Lecture at the Meeting of the German Society for Fat Research, Hamburg, 6th October 1975.Rogers (Ottawa) for kindly providing the low-erucic-acid rapeseed oils.