Human c-myc and normal or mutant T24 H-ras1 genes either linked to the regulatory sequences of the human metallothionein IIa gene or unlinked have been employed individually or in combination to transfect early passage Chinese hamster lung cells. Since the c-myc and H-ras1 genes are present in recombinant plasmids carrying the aminoglycoside phosphotransferase (aph), gene transfectants were selected in the presence of geneticin. A synergistic effect has been observed between myc and H-ras1 genes in measurement of both the number of geneticin resistant colonies obtained and the parameters of morphological transformation and anchorage independence. Out study also demonstrates the ability of truncated myc and ras genes to induce immortalization of hamster cells.