In existing mouse models for malignant brain tumors, genes with no proven pathogenical relevance for humans have been used. Coexpression of platelet-derived growth factor (PDGF) and PDGF receptors suggests an autocrine mechanism of growth factor stimulation in the development of brain tumors in man. A murine retrovirus coding for the PDGF B-chain was, therefore, used to induce brain tumors in mice. Of 35 mice who received injections, 15 developed brain tumors of oligo- or monoclonal origin. They coexpressed PDGF B-chain and α-receptor mRNA, as expected, from an autocrine mechanism of transformation. Most tumors displayed characteristics of glioblastoma multiforme or of a primitive neuroectodermal tumor, and the consistent expression of nestin suggested that they were all derived from an immature neuroglial progenitor. The results show that an autocrine mechanism of transformation may be an initial or early event in neuro-oncogenesis. The present model provides an ideal system for studies of genetic mechanisms involved in the development of brain tumors.