Bladder cancer is one of the most common cancers worldwide, with the highest incidence in industrialized countries. There are three major histological subtypes of bladder cancer: transitional cell carcinoma (TCC) (> 90%), squamous cell carcinoma (< 10%) and adenocarcinoma (1-2%). The present study was carried out to assess the effects of conferone, a sesquiterpene coumarin isolated from Ferula badrakema, on a TCC subline, 5637 cells. In order to test the effects of conferone, 5637 cells were treated with different concentrations (16, 32, 64, 128 microg/ml) of conferone. The results indicated that conferone did not have any significant cytotoxic effect on these neoplastic cells. To determine the combining effects, the cells were cultured in the presence of different concentrations of conferone (16, 32, 64, 128 microg/ ml) and vincristine (30, 40, 50 microg/ml) in combination. The morphological changes were then observed and cytotoxicity effects were studied using the MTT assay 24, 48 and 72 h following drug administration. The cells were more rounded and granulated after treatments with both drugs in comparison to vincristine only. The results of the MTT assay confirmed the morphological observations. After 48 h of combined treatment with 40 microg/ml vincristine and 16 microg/ml conferone, the cytotoxicity of vincristine was increased by 23.6%.