Comparison of the growth-promoting effect of nasturtium seed oil, containing 86% of erucic acid, with that of rapeseed oil (about 50% erucic acid), as well as determination of the effect of erucic acid on growth, or of fat mixtures containing tri-erucin, has shown that the unfavourable growth obtained with rapeseed oil must be ascribed to the erucic-acid content of this oil.