Though many laboratory and clinical trials of tumor heating or cooling have been made for the treatment of intracranial tumors, the effects have been reported to be incomplete and unsatisfactory in most of the cases. In 1965, Popovic et al. reported that differential hypothermia, to keep an experimental tumor normothermic under general body hypothermia, showed more marked effect on the tumor in experimental animals. In the present study, the author investigated the uptake of intravenously administered RISA and sodium fluorescein to the brain tissues of mongrel dogs, in which cold induced lesions were made by a stick of dry ice bilaterally on the cerebral cortices. RISA was administered to those dogs intravenously 3 to 4 hours after making the lesions, while sodium fluorescein 30 to 40 minutes prior to the end of the D.H. treatment, respectively. Under total hypothermia (rectal temperature: 21-23℃), the D.H. treatment was performed for 5 hours. It was found that the uptake of RISA through the cerebral blood vessels was increased in and around the cortical lesions. This change was observed only during the D.H. treatment, and disappeared after the body temperature returned to the normal level. In the observation of sodium fluorescein at the tissue level increased permeabiliity of blood vessels was also observed.