The limited availability of enriched populations of oligodendroglial progenitors has impeded the exploration of the complex spatio-temporal mechanisms which dictate the chemical “language” of their biology. We have developed a technique to prepare homotypic aggregates of oligodendrocyte progenitors called “oligospheres.” These were obtained using various approaches (sieving, Percoll gradient separation and differential adhesion) to purify oligodendroglial progenitors from newborn rat brain. Culturing cells in a mixture of N1 defined medium and conditioned medium from the B104 neuronal cell line in the absence of adhesive substrate allowed to expand routinely and extensively for several months, the oligodendrocyte progenitor population. Under these conditions, the resulting population consisted of 98% GD3-positive/GFAP-negative cells. After dissociation and plating on polyornithine coated substrates, in the presence of low (2%) or high (20%) serum, oligosphere-derived oligodendrocyte progenitors were induced to differentiate into GalC-positive oligodendrocytes or GFAP-positive astrocytes, respectively. When transplanted into the newborn shiverer mouse brain, oligospheres were able to provide a focal reservoir of migrating and myelinating cells. Oligospheres are thus ideal tools for exploring the biological and molecular events of the oligodendrocyte lineage both in vitro and in vivo.