Background: Maple syrup urine disease (MSUD) is an autosomal recessive inborn error of metabolism caused by deficiency of the activity of the mitochondrial enzyme complex branched-chain ketoacid dehydrogenase, leading to accumulation of the leucine, isoleucine and valine, branched-chain amino acids (BCAA). Neurological sequelae are present in most patients, but the mechanisms underlying the neurotoxicity in this disorder are yet unclear. Objectives: We studied the activity of acetylcholinesterase in hippocampus, striatum, cerebral cortex and serum of rats submitted to an animal model of MSUD. Material and methods: For acute administration, three injections (1 h interval) of BCAA pool or saline were given subcutaneously to rats on postnatal day (PD) 10 or 28. For chronic administration, two injections (12 h interval) of BCAA pool or saline were given subcutaneously starting at PD 7 for 21 days. One hour (acute) or twelve hours (chronic) after the last injection, the animals were killed by decapitation, the brain was removed and serum was collected; acetylcholinesterase activity was measured.