Proliferating precursors to the distinct cell types constituting the mammalian brain can be identified by the presence of the nestin intermediate filament. We report the establishment of a nestin-positive cell line, HiB5, from embryonic precursor cells to the rat hippocampus. Since it was immortalized using the temperature-sensitive allele tsA58 of SV40 large T antigen, these cells grow continuously at 33 degrees C, but not at 39 degrees C, the body temperature of rodents. To test their developmental capacity, HiB5 cells were implanted into both the neonatal hippocampus and cerebellum. The cells integrated into the host tissue and acquired morphologies characteristic of the neurons and glial cells found at the implant site. HiB5 cells might thus be useful in characterizing the signals regulating cell type determination in the mammalian brain.