A synthetic light-activated chlorin with photodynamic activity. Upon systemic administration, temoporfin distributes throughout the body and is taken up by tumor cells. Upon stimulation of temoporfin by non-thermal laser light (at 652 nm), and in the presence of oxygen, this agent produces highly reactive short-lived singlet oxygen and other reactive oxygen radicals, resulting in local damage to tumor cells. This may kill tumor cells and may reduce the tumor size.