Transfection and stable transformation of adult mouse Schwann cells with SV-40 large T antigen gene. Cultured Schwann cells derived from adult mouse dorsal root ganglia and peripheral nerves were transfected with a plasmid containing SV-40 large T antigen gene, and 25 colonies of stable transformants were obtained, one of which was expanded and recloned. This transfected cell line, designated MS1, expressed SV-40 large T antigen and showed continuous cell growth with a doubling time of 27 hours. The MS1 cells had distinct Schwann cell phenotypes such as S-100 protein, laminin, 2',3'-cyclic nucleotide 3'-phosphodiesterase and P0 protein, as shown by immunofluorescence microscopy. When MS1 cells were exposed to dibutyryl cyclic adenosine-3',5'-monophosphate (dbc AMP), they extended long bipolar processes two- to ten-fold longer than those of untreated MS1 cells and frequently formed whorl-like alignments similar to palisade formations or organoid patterns observed in human Schwannomas and neurofibromas. These results suggest that transformed Schwann cells can be a useful model for analyzing regulatory mechanisms of Schwann cells, neuron-Schwann cell interactions and experimental Schwann cell neoplasms in vitro. 