The effect of partial isomerization of dietary alpha-linolenic acid on the monoaminergic neurotransmitters in piglets was studied. After feeding the animals for 14 days with diets containing or not trans alpha-linolenic acid, neurotransmitters related to the monoaminergic function were quantified in the frontal cortex and in the hippocampus. The partial isomerization of dietary alpha-linolenic acid resulted in increasing endogenous monoamine levels in the frontal cortex (+55% for dopamine) and was related to a very low incorporation of trans polyunsaturated fatty acids. However, feeding animals with a diet in which the imbalance generated by the isomerization of alpha-linolenic acid was corrected succeeded in reducing the levels of monoamine in the frontal cortex but not in the hippocampus. These results suggest that the dietary trans fatty acids may act on the endogenous neurotransmitter levels during the brain development. Further work is needed to clarify the molecular mechanisms involved.