The expression of oncogenes in well-characterized B16 melanoma and UV-2237 fibrosarcoma cell variants that exhibit distinct metastatic properties was explored. The search for the expression of 11 different oncogenes revealed that the major oncogene in those two tumor systems is the Kirsten-ras (ki-ras). The results indicate that the amounts of specific ki-ras mRNA and the p21 protein are similar in both low- and high-metastatic counterparts. These results suggest that in these systems there is no apparent direct correlation between the amount and expression of the major cellular oncogene so far identified and the metastatic potential of these tumor cells.