Five children with retinoblastoma were treated using an argon laser photocoagulator and a hematoporphyrin derivative. Fluorescein angiography after the photoradiation revealed hypofluorescence of the tumor, indicating obstruction of the tumor vessels. Histopathologic examination of the tumor from the patient treated with photoradiation therapy and without other treatments revealed that tumor cells were destroyed and angionecrosis took place. It was thought that the tumor smaller than 4 disc diameters might be destroyed by this treatment alone. In the case of a larger tumor, photoradiation therapy plus radiotherapy was necessary, but the dose of radiation could be reduced. The side effects embraced vitreous hemorrhage and retinal damage in the nontumorous part when photoradiation was excessive; use of Goldmann's three-mirror funduscope was indispensable to avoid excessive photoradiation. Based on the present experience the following methods may be recommended: 3 days after intravenous administration of 2.5 mg per kg of the hematoporphyrin derivative, photoradiation is carried out using an argon laser of 2-mm spot size and the intensity of 200 mW for 10 minutes. If the tumor remains viable, repeat the photoradiation with 100 mW intensity plus the hematoporphyrin derivative at one-month intervals.