Fos oncoproteins transform cells by functioning as transcription factors. Over-expression of c-fos results in minimal morphological transformation while the two viral isolates, FBJ and FBR v-fos, result in full morphological transformation. Fos-transformed cells are serum dependent for proliferation but not for morphological transformation. To identify Fos target genes which might be involved in morphological transformation we screened a cDNA library constructed from RNA isolated from serum starved FBR-transformed cells with cDNA probes prepared from both FBR-transformed cells and untransformed parental fibroblasts, 208F. We identified 10 genes which are differentially expressed between FBR and 208F cells. One is a novel gene. Nine are upregulated in c-fos- and FBJ-transformed cells and also in mutant c-Ha-Ras-transformed 208Fs. All nine of the upregulated genes have been associated previously with invasion or metastasis. We demonstrate that the FBR-transformed cells are invasive in an in vitro assay and that their ability to invade is enhanced by platelet derived growth factor. We conclude that the fos oncogenes target genes involved in morphological transformation, and invasion.