We used mitotic chromosomes isolated from a human EJ bladder carcinoma cell line for morphological transformation of mouse C127 cells. These chromosome-mediated transformants were analyzed for cotransfer of markers syntenic with c-Ha-ras-1 on human chromosome 11. We also used cloned, dispersed human DNA repeats, in a general mapping strategy, to quantitate the amounts and molecular state of human DNA transferred along with the activated c-Ha-ras-1 gene. In situ hybridization was used to visualize the physical state of the transfected human chromatin. The combined use of these various techniques revealed the occurrence of both chromosomal and DNA rearrangements. However, our analysis also demonstrated that, in general, very substantial lengths of DNA are transferred intact. Closely linked markers are likely to cosegregate. Therefore, these transformants should be invaluable sources for the complete molecular cloning of isolated fragments of the short arm of human chromosome 11.CMGT is a long-established technique which enables variable subchromosomal lengths of DNA to be transferred efficiently to appropriate recipient cells (reviewed by McBride and Peterson [23]). Exploitation of this and other somatic cell techniques has been compromised by the limited availability of dominantly acting selection systems (23,31,39). We can now describe the use of a new class of dominant selectable markers in CMGT, the human oncogenes. Mitotic chromosomes derived from the human EJ bladder carcinoma cell line induced morphological transformation, anchorage-independent growth, and tumorigenicity in mouse C127 cells