Oligodendrocytes in different central nervous system regions have dissimilar morphologies. In order to find out if immature oligodendrocytes develop different phenotypes spontaneously, neonatal spinal and cerebral rat oligodendrocytes were cultured in vitro in the absence of neurons. The results show that spinal oligodendrocytes tend to develop a bipolar structure with few processes, while cerebral cells tend to become multipolar with many processes. A similar spinal-cerebral difference was seen in oligodendrocyte-enriched cultures. Hence, spinal and cerebral oligodendrocytes develop partly different morphologies in vitro.