Metallothioneins (MTs) are induced by various stimuli and probably confer drug resistance in tumor cells in vitro. To investigate whether MT expression in lung cancer is induced by chemotherapy, ninety-seven surgical specimens from patients who had or not received chemotherapy containing cisplatin, were stained immunohistochemically for MT. In untreated tumors, 23% (15/64) of all tumors and 27% (15/56) of non-small-cell carcinoma (NSCLC) stained positive, while all eight small-cell carcinoma (SCLC) were negative. In treated tumors, 52% (17/33) of all tumors, 80% (12/15) of NSCLC and 28% (5/18) of SCLC stained positive. The proportion of positively-stained tumors was significantly higher in treated NSCLC compared with untreated NSCLC (P = 0.0005) and treated SCLC (P < 0.005). Our results indicate that MT expression increases following chemotherapy and that such expression may confer during resistance in lung cancer, especially NSCLC.