An animal model to investigate the invasive and metastatic properties of human bladder transitional cell carcinoma (HTCC) was established. Two long-term HTCC cell lines (RT4 and EJ) and one HTCC cell line derived in our laboratory (LD-71) were tumorigenic when injected s.c. into nude mice but had little potential to invade locally or metastasize before the animals succumbed to tumor burden. Experimental lung metastases were, however, observed in approximately 60% of animals given injections of RT4 or EJ cell lines in the tail vein. The cells were also implanted transurethrally into the urinary bladders of athymic mice. RT4 cells, which were originally isolated from a superficial papillary tumor, produced histologically noninvasive tumors after transurethral inoculation with no evidence of metastasis. In contrast EJ cells, which were originally isolated from a more aggressive tumor, produced invasive tumors in nude mouse bladders and metastasized to the lungs spontaneously. The invasive cell line LD-71 was weakly tumorigenic and was successfully implanted into the bladder on only one of five attempts. The human origin of the implanted tumors was documented by Southern blot analysis using human repetitive DNA as a probe. The results indicate that the site of injection strongly influences the behavior of the resulting tumors and that intravesical implantation of these HTCC cell lines produces pathological expression of invasiveness and metastatic potential.