We established clonal cell lines from fetal brains and a cerebellum of p53 deficient mice. In this paper, stem cell lines are selectively described. FBD-103a line generates neurons, astrocytes and oligodendrocytes. 2Y-6fl line generates neurons and astrocytes. 2Y-3t line generates neurons and oligodendrocytes. FBD-104 line generates astrocytes in conventional culture, but formation of spheres in suspension culture gives the line the capability to produce neurons in addition to astrocytes. Analyses of these lines were done mainly by limited dilution cloning, immunostaining and Western blotting. Some factors in culture medium and kidney were shown to regulate differentiation of the stem cell lines.