OBJECTIVE The ongoing search for the enhancement of efficacy of photodynamic therapy stimulates the interest in molecular mechanisms of the response to the treatment. Looking for the cell line suitable for investigation of cellular response both in vivo and in vitro, we evaluated phototoxicity of m-tetrakis-(3-hydroxyphenyl)-chlorin (mTHPC) on viability of Lewis lung carcinoma (LLC1) cells in vitro, growth of murine transplantable tumor, and mice survival. METHODS LLC1 cell culture and male C57BL/6 mice bearing Lewis lung carcinoma were used for the experiments. Photodynamic treatment was mediated by m-tetrakis-(3-hydroxyphenyl)-chlorin as a photosensitizer. Light emitting diode array was used for illumination. The effect of the photodynamic treatment was evaluated by comparison of viability of control and treated cells, growth of tumors, and survival of the control and treated mice. RESULTS In vitro, a cytotoxic dose inducing a reduction in viability of LLC1 cells by 50% was achieved at 60 mJ/cm(2) and approximately 400 ng/mL of the photosensitizer, or 30 mJ/cm(2) and 600 ng/mL of mTHPC. Both the concentration of the photosensitizer and duration of light exposure were significant determinants of cytotoxic effect. In vivo, an injection of 0.25 mg/kg of mTHPC to mice bearing Lewis lung tumor and illumination at 120 J/cm(2) taking place after 24 h significantly inhibited tumor growth and prolonged mice survival. However, the tumors regained their growth potential after 9 days. CONCLUSIONS Photodynamic treatment mediated by m-tetrakis-(3-hydroxyphenyl)-chlorin had a significant effect on LLC1 cells in vitro and growth of Lewis lung carcinoma in vivo.