Recent clinical successes of small-molecule epidermal growth factor receptor (EGFR) inhibitors in treating advanced non–small cell lung cancer (NSCLC) have raised hopes that the identification of other deregulated growth factor pathways in NSCLC will lead to new therapeutic options for NSCLC. Met, the receptor for hepatocyte growth factor, has been implicated in growth, invasion, and metastasis of many tumors including NSCLC. To assess the functional role for Met in NSCLC, we evaluated a panel of nine lung cancer cell lines for Met gene amplification, Met expression, Met pathway activation, and the sensitivity of the cell lines to short hairpin RNA (shRNA)–mediated Met knockdown. Two cell lines, EBC-1 and H1993, showed significant Met gene amplification and overexpressed Met receptors which were constitutively phosphorylated. The other seven lines did not exhibit Met amplification and expressed much lower levels of Met, which was phosphorylated only on addition of hepatocyte growth factor. We also found a strong up-regulation of tyrosine phosphorylation in β-catenin and p120/δ-catenin in the Met-amplified EBC-1 and H1993 cell lines. ShRNA-mediated Met knockdown induced significant growth inhibition, G₁-S arrest, and apoptosis in EBC-1 and H1993 cells, whereas it had little or no effect on the cell lines that do not have Met amplification. These results strongly suggest that Met amplification identifies a subset of NSCLC likely to respond to new molecular therapies targeting Met. [Cancer Res 2007;67(5):2081–8]