Hematoporphyrin is a photosensitizer. Hematoporphyrin (3 μM) increases oxygen consumption and decreases the respiratory control ratio (RCR) in irradiated isolated rat liver mitochondria. It induces DNA breaks in cell-free assays, but not in human HeLa cervical cancer cells, in a light-dependent manner when used at a concentration of 6 μM. Hematoporphyrin (12 μM) decreases the survival of irradiated, but not non-irradiated, HeLa cells. Hematoporphyrin (5 mg/kg) decreases growth of subcutaneous Yoshida AH-130 hepatoma tumors in rats when administered with radiation.