The animal experiments suggest that small white mice with sarcoma and liver cancer, in which HPD and fluorescein sodium are injected into the abdominal cavities, can produce intenser fluorescence in the tumors than in the normal tissues when they are irradiated by a He-Cd laser, and various types of lights have different effects on the small white mice injected with HPD: sunlight has the greatest effect, then the 100 W electric light, and HPD has some side-effects on the livers of small white mice.