Intracranial hemorrhage was induced in rats by low potent substances, glucose, NaCl and Na₂SO₄, intraperitoneally injected in enormous amounts, that is, 2800 mOsmol/L (J. Toxicol. Sci. 5, 290, 1980). The present study was undertaken to examine a mechanism of the above-mentioned phenomenon in detail from the aspects of the disturbance of water-electrolyte balances and the change in blood osmolality. After administration of hypertonic solutions, blood and abdominal fluid were obtained at intervals of 5 to 15 min and at death. Hypertonic solutions injected intraperitoneally induced rapid exchange in water and solutes across the peritoneum, thus causing an increase in abdominal fluid volume and plasma osmolality. Most interesting was the fact that a marked potassemia was produced and that the value of plasma potassium reached 10 mEq/L at death in all of groups of intraperitoneally injected rats. Thus, it is clear that the intracranial hemorrhage is accompanied by an increase in the plasma concentration of potassium which does not always run parallel with an increase in sodium concentration and osmotic pressure in rat plasma.