The identification and isolation of oncogenes capable of inducing malignant transformation on transfection into rodent cells from human tumour cells has opened the possibility of deciphering the processes involved in human carcinogenesis. With the exception of three human lymphomas¹, the human transforming genes so far identified have been detected in established tumour cell lines^1–8, raising the possibility that they might have been activated during in vitro manipulation of the cells. However, we report here that unmanipulated human solid tumours, including carcinomas of the colon (two), lung and pancreas and an embryonal rhabdomyosarcoma, also contain dominant transforming genes. The carcinomas of the lung and pancreas and the rhabdomyosarcoma possessed a common oncogene which, like that isolated from human LX-1 lung carcinoma cells⁹, shares sequences with the onc gene of the Kirsten strain of murine sarcoma virus (MSV). We also show that several other human tumour cell lines, including those established from carcinomas of the colon (A2233), lung (A427 and A2182), gall bladder (A1604) and urinary bladder (A1698), possess the same oncogene. Thus a variety of human tumours, regardless of their clinical manifestations, contain a common transforming gene.