In a recent review on the role of fats in human nutrition Vergroesen and Gottenbos (1975) emphasize, that the presence of erucic acid isomers in hydrogenated marine oils (HMO) may constitute a toxicological problem as serious as erucic acid in rapeseed oil (RSO). On the contrary Christophersen et al. (1976) stress, that these fatty acids in HMO represent a minor toxicological problem, and that conclusions drawn from HMO to RSO are questionable. Preliminary studies at our institute indicate lipidosis in the heart both in rats fed RSO and HMO, containing equivalent amounts of erucic acid and erucic acid isomers respectively. Further experiments of longer duration are performed with HMO and RSO in order to compare the effect on the heart, especially in relation to the formation of cell necrosis.