Abstract: BACKGROUND ＆ AIM: To investigate the role of MT_ 3 in transitional cell carcinomas of bladder and the possible relation with MDR_1. MATERIALS AND METHODS: Using RT_PCR technique, the expressions of MT_3 and MDR_1 mRNA in 11 specimens from normal bladder mucosa and 23 specimens from bladder transitional cell cancer(BTCC) were measured. RESULTS: MT_3 and MDR_1_positive expression rates were found in 0 and 9.1％ in normal bladder mucosa ,respectively .But they were 78.3％ and 56.5％ in 23 BTCC specimens ，respectively. The positive rate was significantly higher in BTCC specimens than in normal tissue (P<0.05) .The expressions of MT_3 and MDR_1 were not related with the grade ,stage and recurrence after postoperative intravesical chemotherapy. CONCLUSION: MT_3 mRNA could not be identified in normal bladder mucosa, but highly expressed in bladder neoplasm，MT_3 might be used as a tumor marker.

Key words: bladder neoplasms, metallothionein, multidrug resistance