A homotransplantable tumour (LY) and cell lines (LY-PPB6 and LY-H12) were established from a spontaneous malignant peripheral nerve sheath tumour (PNST) of the uterine cervix of an F344 rat. Primary and LY tumours consisted of oval or spindle-shaped cells arranged in a flatfield or streaming fashion, and indistinct nuclear palisades were seen. Immunohistochemically, neoplastic cells reacted to vimentin, S-100 protein, neuron-specific enolase (NSE), myelin basic protein (MBP), and glial fibrillary acidic protein (GFAP) in varying degrees, indicating neurogenic derivation. LY-PPB6-induced tumours in syngeneic rats developed cellular whorling patterns reacting particularly strongly to S-100 protein, NSE, MBP and GFAP. Nerve growth factor (NGF) mRNA expression was shown in LY-PPB6 cells by the reverse transcription-polymerase chain reaction (RT-PCR). By contrast, LY-H12 had a normal chromosomal number of 42, and did not produce tumours when injected into syngeneic rats. LY-H12 cells reacted to vimentin and alpha-smooth muscle actin (alpha-SMA), and the alpha-SMA-positive cell number was increased dose-dependently by the addition of transforming growth factor (TGF)-beta1, indicating a myofibroblastic nature. LY-PPB6 cells were neoplastic with properties of PNS cells, whereas LY-H12 cells were non-neoplastic stromal cells showing myofibroblastic differentiation. As TGF-beta1 mRNA expression was shown in both LY-PPB6 and LY-H12 cells by the RT-PCR, the myofibroblastic phenotype of LY-H12 cells may be mediated by paracrine or autocrine signalling in tumour tissues. LY-PPB6 and LY-H12 may prove useful for studies on the pathobiological nature of neoplastic cells and interactions between neoplastic and stromal cells in PNSTs.