Myelin was isolated from the brain stem region of rats which were administered chronically with ethanol either through intragastric tubing (8gm/kg) for 3 weeks or by giving a 15% ethanol ad lib as drink for 1 year. The protein, phospholipid and cholesterol content and the acyl group composition of major phosphoglycerides of myelin were examined. Based on the protein content, there was less myelin isolated from the chronic alcoholic brain samples as compared to controls. Intrinsic changes in membrane components were observed. The phospholipid to protein ratio of myelin was approximately 20% lower in the group subjected chronically to ethanol by drink and 10% lower in the group given ethanol through intubation technique. The cholesterol to protein ratio was also lower in the group given ethanol as drink but the intubated group was not different from controls. Changes in phosphoglyceride acyl group composition were also observed. In general, there was an increase in the proportions of 16:0, 18:0 and 18:1 and a decrease in 20:1, 20:4 and 22:6. The acyl group changes reflected an increase in cellular phospholipase A2 or a decrease in chain desaturation and elongation activity due to chronic ethanol administration. These changes are also reflective of degenerative changes possibly associated with demyelination.