Because of its cellular complexity and regional heterogeneity, the mammalian central nervous system is not easily amenable for experimental analysis. The study of the developing brain becomes even more complicated because of the differential growth rates of different parts of the brain. Primary culture techniques involving dissociation of discrete regions of the developing brain into component cells offer an excellent opportunity to study the regulation of growth and differentiation of neural cells and to investigate their biochemical, morphological, and physiological behavior under well-defined conditions. Methods are available now to isolate and grow individual classes of neural cells (i.e., neurons, astrocytes, oligodendrocytes), thereby enabling one to study the cellular behavior at the individual level and to uncover the nature of cell-cell interactions that presumably govern cell differentiation.