AbstractChick embryo spinal cord has been explanted at two‐day stages, when few or no cells have formed axons, and cultured for five to seven days. The effects of various culture methods and the presence or absence of other tissues on differentiation have been studied. Many cells with axons and numerous nerve fibers were seen in silver‐stained sections of completely isolated neural tube cultured in a fold of vitelline membrane, as well as in neural tube explanted with adjacent tissues and in isolated neural tube recombined with somites. Electron micrographs of corresponding cultures showed cell bodies similar to those of fairly early nerve cellsin vivoand processes with the structure of axons. Some characteristic differences in cell fine structure and in histological organization among these types of cultures were observed. Isolated neural tube cultured directly on a millipore filter did not survive or differentiate as well. These observations indicate that initial phases of nerve cell differentiation can proceed in organ culture and that there is no specific requirement for interaction with adjacent mesodermal tissues. This system can be used profitably for further investigation of factors controlling various aspects of differentiation in the central nervous sys