We have cloned a 9.5-kbp fragment of an oncogene present in a human fibrosarcoma cell line (HT-1080). The cloned fragment is present in all tested HT-1080-derived transformants, and is different from another fragment of the same oncogene (14 kbp) previously isolated. When both fragments are put together, the construction shows a molecular structure similar to that of the N-ras oncogene present in human neuroblastoma cell lines.