Rabbits were exposed to elemental mercury (Hg°) vapor, methyl mercury (MeHg) and HgCl₂ respectively, and the relationship of mercury concentration in brain to that in blood or cerebrospinal fluid (CSF) was investigated after the termination of exposure. At one day post-exposure, the ratio of mercury concentration in brain (μg Hg/g) to that in blood (μg Hg/g) was approximately 10.0 in Hg° vapor, 0.6 in HgCl₂ and 3.0 in MeHg. The ratio for Hg° vapor was about 10 times higher than that for HgCl₂. In rabbits exposed to Hg° vapor, the ratios of mercury concentration in blood to brain or CSF to brain at 1 day and 20 days after the termination of exposure were compared. The blood to brain ratio showed a decrease to about 1/10 after 20 days, and the CSF to brain ratio, a decrease of about 1/2. The results obtained seems to suggest that mercury is eliminated from the blood and CSF more rapidly than from the brain. In the case of rabbits administrated MeHg, the ratio of mercury concentration in blood to that in brain was almost unchanged at both 1 day and 20 days after the termination of exposure. There did not seem to be any differences in the rates of elimination from blood and brain. The elimination of mercury from CSF was more rapid than from brain because the ratio between the mercury concentration of CSF to that of brain showed a decrease to about 1/3 after 20 days.