Gefitinib ('Iressa, ZD1839) has promising antitumor activity in non-small cell lung cancer (NSCLC). However, patients with advanced NSCLC have few treatment options available if they are refractory to gefitinib. We describe four cases of patients with advanced NSCLC who previously responded to gefitinib and obtained significant tumor regression through retreatment with other cytotoxic agents. Gefitinib might restore chemosensitivity to previously chemorefractory patients.