Purpose: To obtain unambiguous evidence for the putative role of E-cadherin in the selective accumulation of hypericin after intravesical instillation in humans we investigated the accumulation of hypericin in spheroids from 3 clones of the human bladder carcinoma cell line T-24 that express different levels of E-cadherin, as determined by immunohistochemistry and reverse transcriptase-polymerase chain reaction. Materials and Methods: Clones of T-24 cells transfected with the E-cadherin gene were analyzed for E-cadherin expression and 3 cell lines with different expression levels were selected. Spheroids of these cell lines were incubated with 10 mu M hypericin in cell culture medium supplemented or not with fetal calf serum for 2 hours. After the incubation period centrally cut sections were examined by fluorescence microscopy. An imaging software system was used to measure average fluorescence in concentric layers from rim to center. Results: Data showed that in the presence of serum the accumulation of hypericin in spheroids was inversely associated with the level of E-cadherin expressed by the T-24 transfectants used, whereas in the absence of serum differential accumulation of the compound was completely abolished. Conclusions: Spheroids composed of cancer cell lines expressing variable levels of E-cadherin represent an excellent model in which to study the role of intercellular adhesion in bladder cancer. The outcome of this study strongly suggests that E-cadherin is the key mediator in the selective accumulation of hypericin in superficial bladder cancer after intravesical instillation in humans.