Abstract: Objective To screen and identify heterogeneous phenotype-associated genes of human bladder transitional cell carcinoma.Methods Subtractive cDNA libraries was established by means of suppression subtractive hybridization(SSH) on the basis of two human bladder transitional cell carcinoma cell lines(BLZ-211 and BLS-211) derived from the same patient,which had similar changes in chromosomes but different cell phenotypes(in terms of cell shape,susceptibility to 5-Fu and tumorigenic capacity).The positive clones in the library were selected for screening differentially expressed gene fragments by sequence analysis and blasting,and Northern blotting was performed to confirm the differentially expressed genes.Results The subtractive forward and reverse cDNA libraries consisted of 168 and 206 white clones containing 200-700 bp inserts.After differential screening,55 cDNA clones containing 35 different transcripts were obtained,among which 15 were identified by homology analysis as known genes(such as those coding for vimentin,keratin 7,dihydrodiol dehydrogenase and thioredoxin reductase),11 as unknown genes,and 9 as new ESTs(GenBank dbEST database accession number DY505708,DY230447-8,DR008207).Conclusion SSH is a powerful method for identifying differentialy expressed genes between different cell lines or clones,and characterization of the identified genes may provide useful information for understanding the genes responsible for different cell phenotypes.