The effects of undernutrition during suckling on neurochemical and behavioral parameters were investigated in adult rats. Young rats were undernourished by feeding their mothers an 8% (by wt) protein diet from delivery until weaning (d 21). Mothers of control rats were fed a 20% protein diet. After weaning, normal and undernourished rats were fed a 20% protein diet until 90-120 d of age, when the rats were subjected to footshocks of low and high intensity during escape training sessions. The memory of footshock escape learning was measured 24 h later by testing with low and high footshock intensity. Also, two neurochemical changes related to the escape training with high footshock intensity were studied: hypothalamic beta-endorphin release during the training and the increase of amino acid incorporation into protein in brain structures 4 h after training. By means of low shock intensity we observed that undernutrition during suckling causes hyperreactivity to electric shock. By means of high shock intensity we observed that undernutrition abolished the neurochemical changes caused by learning training and abolished the memory of footshock escape learning.