To probe the sensitivity of different NSCLC cell lines to gefitinib, four NSCLC cell lines having a different EGFR status, including A549 (wild-type EGFR), H1975 (L858R and T790M mutation in EGFR exon 21-, PC9 (EGFR exon 19 deletion), and PC9/GR (gefitinib acquired resistant PC9 cells), were exposed to various concentrations of gefitinib (0, 0.625, 1.25, 2.5, 5, 10, 20 and 40 μmol/L) for 48 h. This evidence concerns the gene EGFR and non-small cell lung carcinoma.