Various affects of postnatal undernutrition are being investigated using developing rats as an experimental model. Studies are largely confined to the central nervous system. Neurochemical investigations include effects on synthesis of myelin as well as on the development of neurotransmitter receptor binding systems. Morphological studies include the cellular basis of nutrition related hypomyelination. Neurophysiologic correlates include effects of undernutrition on maturation of the photic evoked responses in the retina (electroretinogram), the optic tract, lateral geniculate bodies, and the visul cortes.