Ethyl alcohol is believed to inhibit the secretion of antidiuretic hormone (ADH) from the neurohypohysis, and an increase in urinary volume and reduction in the extracellular fluid volume may follow. In the case of acute alcohol intoxication, the red cells may be exposed. to the increasing level of the blood alcohol, and are in danger of being oxidized and/or hemolysed, for which the blood glutathione may exert a protective action. The aim of this study is to elucidate the acute effect of alcohol on the hematocrit, assuming that the decreased secretion of ADH will result in an increased value of the hematocrit, and also the change of oxidized glutathione (GSSG) and reduced glutatbione (GSH) of the blood following by the adminstration of alcohol. Albino rats were used throughout the experiment, and a rat was given 50% ethyl alcohol in the dose of l. 5 ml per 100 gm of body weight by the oral intubation. In all the alcohol administered cases, the rat immediately following the intubation became comatose and no voluntary effort to intake food or water was observed for at least twenty hours. The rat was sacrificed first by a strong blow on the head and the thorax was immediately opened. The blood sample for both hematocrit and glutathione was drawn from the thoracic cavity with the heart puncture if necessary after cutting the pulmonary and carotid arteries. The experiment was performed at 1,3,6,12 and 24 hours after the alcohol administration, and hematocrit was determined by the conventional hematocrit centrifuge and reader. The blood GSH was measured by the method of Ellman, and GSSG was measured by the method described by Dohan and Woodward. Controls were set which received the same amount of distilled water in place of alcohol.