The effect of chronic aluminium exposure (25 mg/kg b.wt.) was studied on the lipid composition and various membrane-bound enzymes in different regions of monkey brain. Aluminium (Al) administration caused a significant decrease in the total lipid, glycolipid, and phospholipid content of primate brain. Cholesterol levels and the phospholipid to cholesterol ratio were, however, markedly increased as a consequence of Al administration, thereby indicating a loss of membrane integrity. This was further confirmed when Al treatment was found to have a significant effect on the various membrane-bound enzymes in terms of decreased activities of Na+ K+ ATPase and acetylcholinesterase, along with a decrease in the activity of the myelin-specific enzyme, 2' 3'-cyclic nucleotide phosphohydrolase.