The matrix metalloproteinases (MMPs) are members of a unique family of proteolytic enzymes that degrade components of the extracellular matrix. Significant evidence has accumulated to directly implicate members of the MMPs in tumor invasion and metastasis formation. To investigate the correlation between ras oncogene and MMP gene expression in various tumor cells, we detected mRNAs for the ras, MMP-2 and MMP-9 (72 kD and 92 kD type IV collagenases, respectively) genes in nine human tumor cell lines. The ras gene was expressed in seven cell lines; MMP-2 in three; MMP-9 in two cell lines tested. There was no direct correlation between the ras oncogene and MMP expression. A clear difference in the mRNA expression between MMP-2 and MMP-9 was observed among the cell lines. As an approach to study the effect of the ras oncogene on metastasis, we examined the expressions of MMP-2 and MMP-9 in HT1080 cells transfected with the v-H-ras gene. MMP-9 expression was Significantly enhanced in the ras-transfected HT1080 cells compared with the nontransfectants while ras transfection did not affect the expression of MMP-2. These results suggest the possible inducing effect of the ras oncogene on the metastasis by activation of the MMP-9 gene in HT1080.