The karyotypic profiles of an Ehrlich ascites tumor and of four sublines of this tumor were analysed. The four sublines have been selected for their resistance to daunomycin, adriamycin, vincristine and vinblastine, respectively. All the sublines showed mutual cross resistance to the four agents. Some of the mitoses were stained with conventional Giemsa technique, whereas other mitoses were stained with Giemsa banding technique. The wild-type tumor and the vincristine-resistant tumor were found to be near-tetraploid, whereas the three other sublines were hyper-diploid. A number of marker chromosomes were found. It is concluded that the mutual cross resistance of the sublines is not due to selection of the same cell clone from the wild type tumor.