We have been examining the developmental fates and migrational patterns of the immature cells in the subventricular zone (SVZ) of the mammalian forebrain by labeling postnatal rat SVZ cells by stereotactic injection of replication-deficient murine retroviruses bearing reporter genes. SVZ cells migrate into adjacent white matter, cortex, and striatum, and differentiate into astrocytes and oligodendrocytes. In white matter, they largely differentiate into oligodendrocytes, whereas in gray matter, they differentiate into both oligodendrocytes and astrocytes. In vitro, SVZ cells are multipotential, able to generate both types of glia, as well as neurons. We infer that developmental fates are in part controlled by important environmental cues that the cells encounter during their migration.