The growth of the brain is certainly less affected by undernutrition than the growth of the rest of the body (brain sparing). We inquire whether a similar phenomenon occurs within the brain: whether there are differences in sensitivity to undernutrition amongst the brain's component growth processes. We conclude from our review of the literature that, contrary to popular belief, undernutrition depresses the growth rate of various processes within the brain to the same extent. The much quoted "selective" effect on the cerebellum is not an example of an especially sensitive process. It results from expressing deficits as "% of age control values" and disappears when proper comparisons of depression in rates of growth are made. The one growth process which does at first sight appear to be truly especially sensitive is myelin synthesis, in that undernutrition depresses its rate more than that of other growth processes in brain. However, undernutrition also results in fewer fibres being myelinated, and when rate of myelin synthesis is expressed per myelinated fibre the special sensitivity disappears.