Little is known of the alterations in the neurochemical anatomy of the striatum following neonatal hypoxic-ischemic injury. In an experimental model in rodent, it has been shown that striatal biochemical markers of dopaminergic systems appear to be relatively spared. We sought to define the morphologic correlates of this finding by staining striatal tyrosine hydroxylase (TH)-positive fibers with the immunoperoxidase technique. Since this model is unilateral, it is possible to examine relative changes in the density of TH-positive staining of the striatum at the population level within the same section. We find that in immature animals (3-4 weeks) there is an increase in the relative density of striatal TH-positive staining on the injured side. There is also an increase in the relative density of staining in the nucleus accumbens, in the absence of shrinkage of that nucleus. There is no relationship between the degree of density increase in the striatum, and its degree of shrinkage. This increase in relative density is a persistent change, as it is also observed in adult rats (9-12 weeks). While the functional significance of these findings are unknown, they are compatible with a relative increase in the dopaminergic innervation of the hypoxia-ischemia injured striatum.