We investigated the effect of Bcl-2 expression on the metastatic process of bladder cancer cells by using the Bcl-2-transfected human bladder cancer cell lines (KoTCC-1/BH) and the control vector only-transfected cell line (KoTCC-1/C), which were generated in our previous study (Miyake et al (1998) Oncogene 16: 933-934). When they were injected intravenously into athymic nude mice, KoTCC-1/BH formed more than three times as many tumour nodules in the lungs as did KoTCC-1/C. In addition, tumour progression, including lymph node metastasis and haemorrhagic ascites, was observed to be more advanced after the implantation of KoTCC-1/BH cells into the bladder wall of nude mice than after implantation of KoTCC-1/C cells. These enhanced malignant progression of KoTCC-1/BH cells were well correlated with anti-apoptotic activity under anchorage-independent conditions in in vitro experimental models. In contrast, there were no significant differences among these cell lines in their growth rates both in vitro and in vivo, invasive ability and cell motility. These findings suggest that, if it is overexpressed, Bcl-2 prolongs cell survival under unfavourable conditions encountered in the metastatic process, resulting in the enhanced metastatic potential of bladder cancer.