EPO and CEPO do not interfere with the physiological progress of oligodendrocyte maturation and myelination. P6 mice received i.p. injections of EPO, CEPO or vehicle and were evaluated for MBP or O1 immunoreactivity 24, 48, 72 or 96 h later. We found no difference in the onset of myelination, as shown with MBP staining, between the groups at any time point (A–C). Similarly, we found no difference in O1 immunostaining between groups at any time point examined (D–F). Scale bar, 20 µm.