<i>Objective:</i> Pancreatic islets isolated from mice treated neonatally with monosodium <i>L</i>-glutamate (MSG) were used to study insulin secretion. <i>Material and Methods:</i> Total acetylcholinesterase (AchE) activity of tissue extract was measured as a cholinergic activity marker. Obesity recorded in 90-day-old MSG mice (OM) by Lee index reached 366.40 ± 1.70, compared to control mice (CM) 324.40 ± 1.10 (p < 0.0001). Glucose 5.6 m<i>M</i> induced insulin secretion of 36 ± 5 pg/15 min from islets of CM and 86 ± 13 from OM (p < 0.001). When glucose was raised to 16.7 m<i>M</i>, islets from OM secreted 1,271 ± 215 and 1,017 ± 112 pg/30 min to CM. AchE activity of pancreas from OM was 0.64 ± 0.02 nmol of substrate hydrolyzed/min/mg of tissue and 0.52 ± 0.01 to CM (p < 0.0001). Liver of obese animals also presented increase of AchE activity. <i>Results:</i> These indicate that OM insulin oversecretion in low glucose may be attributed, at least in part, to an enhancement of parasympathetic tonus.