Nineteen-day old rats were fed an essential fatty acid deficient diet for 37 weeks, thereby making them essential fatty acid deficient for at least 24 weeks. The weights of their brains were 33% less than those of rats on control diets. 2. When the deficient rats were rehabilitated for ten weeks on a diet containing 5% by weight corn oil as a source of essential fatty acids, the weights of their brains were still 30% less than those of the controls. 3. Analysis of the brain lipids showed that, there was a large reduction in the proportions of cerebrosides and sphingomyelin in essential fatty acid deficiency. 4. Essential fatty acid deficiency was also characterised by the appearance of a high proportion of eicosatrienoic acid (20:3) and the reduction of arachidonic acid (20:4) and the other essential fatty acids. 5. Rehabilitation for a period of 10 weeks did not reverse these changes in brain composition. 6. It is considered that the feeding of essential fatty acid deficient diet to rats for a prolonged period of time causes retardation of brain maturity and makes the brain resistant to later dietary manipulations.
