The present study is designed to screen the possible effects of sodium orthovanadate therapy on the kinetic parameters of brain membrane-bound and soluble acetylcholinesterase (AChE) forms in alloxan-induced diabetic rats. The diabetic rats were treated with 300 mg/kg sodium orthovanadate orally for 45 days. While diabetes significantly decreased the brain specific activity (V(max)) of AChE soluble form by 42%, it caused a fivefold increase of the K(m) of the membrane-bound form. Furthermore, the activity of brain glutathione-S-transferase (GST) was significantly decreased and this was associated with a remarkable increase in brain lipid peroxidative parameter, thiobarbituric acid reactive substances (TBARS), as compared to sham control. The alterations of both AChE forms observed in diabetic state could be attributed to hyperglycemia and lipid peroxidation that triggered brain dysfunction by disturbing the neurotransmitter acetylcholine level. Administration of sodium orthovanadate reversed the diabetic conditions by lowering the blood glucose level and normalized the blood Hb(A1C) level. It also normalized the levels of brain AChE, GST and TBARS as compared to diabetic state and control. Therefore, vanadate administration could protect against direct action of lipid peroxidation on brain AChE and in this way, it might be useful in the prevention of cholinergic neural dysfunction, which is one of the major complications in diabetes.