AbstractWe have prepared highly purified cultures of rat oligodendrocytes by a modification of the procedure of McCarthy and de Vellis [1980]. By utilizing a substratum derived from lysed glia and a calf serum‐containing medium with a high concentration of transferrin, the oligodendrocyte cultures display a high degree of purity, the ability to survive several months of culture, and a striking ability to produce a myelin‐like membrane. We have examined the production of this myelin‐like membrane using immunocytochemical and biochemical probes as well as an extensive morphological examination at the electron microscopic level. The membrane appears to be produced in a similar developmental pattern to that observed in vivo and it has the structural characteristics of loosely packed central nervous system m