Photodynamic therapy (PDT) has been a promising clinical agent in various types of cancer in recent years. In this study, in vitro nuclear imaging and PDT potential of Es-SubPc (Boron subphthalocyanine) were evaluated in colon adenocarcinoma cell line (HT-29) and human healthy lung fibroblast cell line (WI-38). For this purpose, the Es-SubPc was labeled with I-131 using the iodogen method under the optimum conditions resulting in labeled with high yield (98.9 +/- 1.2%). In addition, the uptake rate of I-131-Es-SubPc was determined in HT-29 and WI-38 cell lines. In comparison to the healthy cell line, the uptake of 131I-Es-SubPc was found to be 2-fold higher in the HT-29 cell line. For PDT studies, both cells were exposed to white light at 30-90 J/cm(2) in the presence of Es-SubPc. The results showed that Es-SubPc was a good PDT agent likely to be used in HT-29 cell line. As a result, Es-SubPc can be promising nuclear imaging and PDT agent for colon carcinoma.