Methods are described for maintaining postnatal mouse cerebellar cells in monolayer culture, and for identifying granule cells in such cultures. Cells from cerebella of 7-day-old mice are dissociated with trypsin and DNAse, then plated at 1-1.5 X 10(6) cells/35 mm dish in a high-potassium modification of Hams F12 medium plus 10% fetal calf serum. Under these conditions, cells grow either singly or in small clumps, and develop complex meshes of single fibers and fiber bundles over a period of several days. Granule cells are identified by a combination of several criteria including their size, shape and relative proportion of the total cell population as determined by phase contrast and scanning electron microscopy; nuclear morphology, demonstrated by transmission electron microscopy, and failure to take up [3H]gamma-aminobutyric acid (GABA) in the presence of several other cell types which do, shown by autoradiography.