We have shown previously that intravenous infusions of insulin, known to induce glucoprivic hunger, and of insulin combined with glucose, known to induce satiety, produce in the VMH and PVN of Wistar rats monoaminergic changes that differ from those related to spontaneously occurring hunger and satiety, while the genetically obese Zucker rat is totally resistant to the behavioural effects of insulin and insulin + glucose infusions. In the present study, the impact of these infusions on VMH and PVN monoamines in obese Zucker rats was assessed using microdialysis. Monaminergic changes (increase in DOPAC and 5-HIAA and decrease in DA and 5-HT) were quite similar in obese rats to those we found in normal rats when insulin was infused. In contrast, changes in 5-HT or DA in response to insulin and glucose were quite different in the Zucker rat. Monoaminergic changes related to meals were more dramatic in the Zucker rat and so were able to reverse the background changes produced by the insulin infusion. These data confirm the idea that the effect on monoamines of spontaneously occurring hunger and satiety is different from the effect on monoamines by insulin and glucose-induced hunger and satiety. The results show disturbances of the obese Zucker rat related both to insulin and to hypothalamic monoamines that may be involved in the hyperphagia and obesity of this model.