We have used the polyoma middle T oncogene to immortalize cells from rat embryo encephalon. Immunostaining experiments with monoclonal antibodies demonstrated that the cells of one of the obtained lines, named CEINGE CL3, are stained by anti-vimentin and anti-S100 antibodies, are not stained by anti-neurofilaments (NF) or anti-glial fibrillary acidic-protein (GFAP) antibodies. Only a subset of the CEINGE CL3 cells (20-30%) is stained by an anti-galactocerebroside antibody. Northern blot analysis demonstrated that these cells express low levels of proteolipid protein mRNA, whereas polymerase chain reaction (PCR) amplification failed to evidentiate the presence of both NF and GFAP mRNAs. Either retinoic acid or forskolin treatments or a combination of them are able to induce morphological changes that are accompanied by a complete growth arrest.