The brain/blood, liver/blood, and heart/blood ratios of acatalasemic mice after intraperitoneal injection of metallic mercury or after exposure to metallic mercury vapor were significantly higher than those of normal mice. These ratios of normal or acatalasemic mice after injection with metallic mercury or exposure to metallic mercury vapor were significantly higher than those of normal and acatalasemic mice injected with mercuric ion. The amount of metallic mercury exhaled from acatalasemic mice injected with metallic mercury was greater than that from normal mice, indicating that the level of metallic mercury in blood of the former was higher than that of the latter. Actually, metallic mercury in the blood of acatalasemic mice injected with metallic mercury is higher than that in the blood of normal mice, suggesting that metallic mercury is easily transfered from blood to brain, liver, kidney, and heart.