A 54-year-old woman with lung adenocarcinoma which has EGFR point mutation at exon 21 initially improved by administration of gefi tinib. Lung lesions responded to gefi tinib at 250 mg, but central nervous system lesions, such as carcinomatous meningitis and brain metastasis occurred. The therapy was changed from gefi tinib to erlotinib at 150 mg, resulting in remarkable improvement of carcinomatous meningitis and brain metastasis improved dramatically. We hypothesized that the effective concentration of the clinical dose of erlotinib in the CSF is higher than that of gefi tinib.