The development of kinase inhibitors is revolutionizing cancer treatment. Assessing the oncogenic potential of individual kinase activities and ensuring that a drug of interest acts by direct inhibition of its putative target kinase are clear priorities. We developed a genetic strategy to selectively inactivate the catalytic activity of kinases. This approach generates isogenic cells in which a given kinase gene is expressed but is devoid of enzymatic activity. As a model to test this approach, we chose the MET receptor, which is involved in multiple cancers and is the focus of several therapeutic efforts. The exon encoding the ATP-binding site of MET was deleted from the genome of colorectal, bladder, and endometrial cancer cells. The derivative isogenic cells expressed a kinase-inactive Met (MET-KD) and were completely unresponsive to its ligand hepatocyte growth factor (HGF), indicating the exclusivity of this ligand-receptor axis. The in vivo tumorigenic potential of MET-KD cells was reduced but could be partially restored by HGF, suggesting that concomitant targeting of the receptor and its ligand should be therapeutically exploited. A reportedly selective Met-kinase inhibitor (SU-11274) markedly affected the growth of MET-KD cancer cells, indicating this compound exerts its effects not only through the intended target. The genetic strategy presented here is not limited to kinase genes but could be broadly applicable to any drug/protein combination in which the target enzymatic domain is known.