Oligodendrocytes are largely generated postnatally during mammalian CNS development. We have used a variety of antibodies to label immature neuroectodermal cells and developing oligodendrocytes in several areas of the rat CNS. Antibodies included those to GD3 ganglioside, a characteristic glycolipid of immature cells; carbonic anhydrase (CA), contained primarily in oligodendrocytes; and galactocerebroside and myelin basic protein, myelin components. Several aspects of oligodendrocyte development were examined: changes in shapes of immature cells with respect to time and to location within the brain, the sequential acquisition of the various markers, and possible sites of origin and pathways of precursor cell migration. Our observations suggest that oligodendrocytes in the forebrain and cerebellum arise from cells of the subventricular zone (SVZ) adjacent to the ventricles and migrate into and through nearby white and gray matter. During maturation, there are distinct patterns of morphological changes that correlate with time, locations of the cells in the brain, and acquisition of specific markers.