The presence of oligodendrocyte precursor cells which cannot be removed from primary cultures by antibody-dependent techniques complicates the interpretation of transplantation experiments designed to examine the potential of astrocytes to influence remyelination (Blakemore et al.; Glia 13:79-91, 1995). In the present series of experiments we have investigated the use of the antimitotic cytosine arabinoside to eliminate oligodendrocyte precursors from mixed glial cell cultures following immunolytic removal of both oligodendrocytes and oligodendrocyte progenitors using A2B5 and O4 monoclonal antibodies. Our results indicate that not all oligodendrocyte precursors are involved during the subsequent regeneration of oligodendrocytes since a population of precursors survive 3-day and 12-day exposure to cytosine arabinoside. Maintaining immunolysed cultures in serum-free medium containing cytosine arabinoside for 23 days, removed the potential to generate large clones of oligodendrocytes both in vitro and following transplantation. However, a small number of oligodendrocyte precursors survived this treatment and generated single oligodendrocytes in vitro and isolated clusters of oligodendrocyte remyelination following transplantation. Overall, these results indicate that oligodendrocyte precursors have considerable potential to generate oligodendrocytes, but, since they can also survive for long periods in a quiescent state, their complete elimination from immunolysed astrocyte cultures by the use of an antimitotic is unreliable, if not impossible.