Oligodendrocytes and Schwann cells use diverse regulatory elements to transcribe myelin basic protein (Mbp). For example, an enhancer 9.0 kb upstream of Mbp (MbpSCE1) activated either the proximal Mbp or hsp68 promoters only in Schwann cells in transgenic mice. Here, we analyze MbpSCE1 in vitro and in vivo and show that MbpSCE1 also activates another myelin gene, Mpz, specifically in Schwann cells in transgenic mice. Surprisingly, although MbpSCE1 behaves as an enhancer in Schwann cells, we show here for the first time that it also activates transcription robustly in cultured oligodendrocytes, but only from its original genomic position. Diverse nuclear proteins binding at distinct combinations of DNA elements in the two cell types may account for cell-specific MbpSCE1 function. A further surprise is that MbpSCE1 activation does not depend on consensus binding sites for the myelin-associated PPARbeta or Krox 20 transcription factors. Finally, chromatin context augments activation of MbpSCE1. Therefore, MbpSCE1 is active in both Schwann cells and oligodendrocytes, but by diverse mechanisms.