Weanling female rats randomly divided into three groups were fed a basal alipidic diet added with 10% (w/w) corn oil, soybean oil or linseed oil. After thirty and ninety days of dietary treatment the rats were killed and the fatty acid composition of brain, optic nerve and visual cortex was determined. The results demonstrate a different sensitivity to the diet of the different structures examined and, for the linseed oil treated rats, a strong decrease in the proportions of the total (n-6 + n-3) polyunsaturated fatty acids in all the structures examined.