The ras oncogene family has been implicated in the growth and development of a high percentage of human tumours. However, the biochemical role of p21 ras the protein encoded by this oncogene, is not well defined. Therefore, the effects of p21 ras transformation of murine fibroblasts on cellular signal transduction were investigated. The study utilised a clone of NIH3T3 cells which overexpressed the p21 N-ras protooncogene in the presence of a glucocorticoid inducer. Overexpression of p21 N-ras in this cell line results in uncontrolled cell proliferation and transformation. The effects of transformation on growth factor mediated signal transduction pathways were studied