The retroviral oncogene v-src arose by transduction of the cellular gene c-src. The similarity between these genes raised the possibility that c-src might be able to elicit neoplastic growth. We explored this by constructing a chimeric plasmid that allows the expression of chicken c-src. A rat cell line containing ten times the normal intracellular level of pp60c -src was isolated after transfecting rat-2 cells with the chimeric DNA. These cells produce the protein encoded by c-src ( pp60c -src) in quantities at least three times greater than required to achieve transformation by the product of v-src ( pp60v -src). The cells remain phenotypically normal, contain actin cables, and do not grow in soft agar. However, transfection of the cell line containing elevated cells of pp60c -src or Rat-2 cells with a molecular clone of v-src produces cells that exhibit properties of biologically transformed cells: round morphology, disrupted actin cables, and ability to grow in soft agar.