We have examined the regulation of neuron-specific gamma-enolase gene (NSE) expression in oligodendrocytes at various steps of their differentiation/maturation. We have demonstrated for the first time that NSE is expressed in oligodendroglial cells in vitro and in vivo, and only at a certain stage of differentiation. A heterogeneity of the gamma subunit was observed in cultured oligodendrocytes and the same one was found in adult rat brain. The level of gamma mRNA increased when precursor cells differentiated into oligodendrocytes. By contrast, no significant change in alpha-enolase gene expression was observed. High NSE (gamma gamma and alpha gamma) enolase activity was detected in cultured oligodendrocytes. Treatment with basic fibroblast growth factor, which stimulates the proliferation of oligodendrocyte precursor cells and reversibly blocks their differentiation, resulted in lower alpha gamma- and gamma gamma-enolase activities in these cells, but it enhanced alpha alpha-enolase activity slightly. These data indicate that gamma-enolase gene expression is associated with the differentiation of the oligodendrocytes and that it is repressed in adult fully mature cells.