N-3 fatty acid deficiency has been related to decreased docosahexaenoic acid (DHA) and increased docosapentaenoic acid (DPA) levels in brain and to learning disadvantages. The influence of n-3 deficiency and supplementation on brain fatty acids and learning were investigated in young rats. Newborn Wistar rats were assigned to three groups of cross-foster mothers. The control group (C) was nursed by mothers that received essential fatty acids during pregnancy and lactation, and the deficient group (D) was nursed by mothers that did not receive those fatty acids. The supplemental group (S) had the same conditions as D, receiving an additional DHA and arachidonic acid supplement during lactation. Cerebral cortex and hippocampus fatty acid composition was examined using thin-layer and capillary column gas chromatography, and learning was measured by passive-avoidance procedure. D brains showed low DHA and high DPA levels, but S brain composition was similar to C. Learning in the S group was unaffected, but in the D group, it was poorer than C. Learning was directly correlated with DHA levels and inversely with DPA levels in brain. Low DHA and high DPA brain levels both were correlated with poor learning. DPA seems not to be a suitable brain functional analogue of DHA, and DHA supplementation reversed both biochemical and learning adverse effects observed in n-3 deficiency.