Recent evidence suggests that insulin-like growth factor-I (IGF-I) acts as a neurotrophic factor in the injured CNS. The role of the related peptide IGF-II is unclear. Therefore, we compared the induction of IGF-II in the developing rat brain following mild or severe hypoxic-ischemic (HI) injuries. Ligation of the right carotid artery of 21 day old rats followed by either 15 or 60 min exposure to 8% oxygen led to mild or severe unilateral damage respectively. Brains were collected at 1 day, 3, 5, 7 and 10 days, post-hypoxia. In situ hybridization showed that the 15 min injury (which produced selective neuronal loss) produced no change in basal IGF-II gene expression. However, the 60 min injury, which resulted in cortical infarction and severe neuronal loss in other regions, led to the induction of IGF-II mRNA mainly in the infarcted cortex, from 5-7 days post-hypoxia. Immunohistochemical analysis of brains collected 10 days after the 60 min injury showed that IGF-II immunoreactivity (IR) was also increased, predominantly in damaged regions, but also in the contralateral hippocampus. IGF-II IR was associated with non-neuronal cells that appeared to be microglial-like cells and astrocytes. Together these data suggest that IGF-II may modulate the response of glial cells during recovery from cerebral infarction.