The tumorocidal effect of hyperthermia was studied in Greene's amelanotic hamster melanoma transplanted into the anterior chamber of rabbit eyes. To achieve optimal depth penetration, hyperthermia was induced with near infrared light of 820–870 nm, during 15 minutes, at a beam diameter of 2.5–6.0 mm resulting in an intermediate level hyperthermia of 45–60°C.At 45°C no tumor destruction occurred, at 50°C the effect varied from no destruction to total thickness tumor destruction. At 55–60°C total tumor destruction with additional lens damage occurred. In comparison photocoagulation with white light revealed only necrosis up to half the tumor thickness.