1. The effects of alcohol on blood oxygen transport properties were studied in rats after a chronic administration of ethanol in drinking water. 2. Ingestion of ethanol provokes an increase in haemoglobin oxygen affinity (at pH 7.4). This is caused by a drop in the MCHC and erythrocyte 2,3-BPG concentration that give rise to a decrease in the 2,3-BPG/Hb ratio. 3. No changes in haemoglobin fractions were observed. 4. The results indicate a depletion in the red blood cell glycolytic pathways. 5. If metabolic acidosis occurs, the expected loss of blood affinity in vivo due to the fall in pH would be compensated by the changes observed in vitro.