The chemokine macrophage inflammatory protein 1alpha (CCL3) is expressed by immune cells in the normal and injured perinatal brain. To determine whether the chemokine receptor CCR5 is a relevant target for CCL3 in the brain, we used RT-PCR and immunocytochemistry to assess changes in CCR5 expression and localization in developing normal and injured rat forebrain. CCR5 protein was expressed predominately by resting and activated microglia until 2 weeks of age. Neonatal hypoxia-ischemia increased CCR5 mRNA expression while causing CCR5 internalization, indicating receptor activation. These data implicate CCR5 in microglial recruitment and activation during brain development and after neonatal brain injury.