Deficiency in n-3 fatty acids is known to disturb the release of dopaminergic neurotransmitters in rat brain. Since isomerization reduces the bioavailability of dietary fatty acids, the effect of the conversion of alpha-linolenic acid into trans alpha-linolenic acid on the dopaminergic neurotransmission was studied. Rats were fed for 21 months with a control diet, a diet unbalanced in cis alpha-linolenic acid and containing trans alpha-linolenic acid or the same diet in which the imbalance was corrected by increasing the levels of cis alpha-linolenic acid. After 6 and 21 months of diet, the fatty acid composition and the amounts of endogenous dopaminergic neurotransmitters was assessed in the striatum, the frontal cortex and the hippocampus. The isomerization of a part of dietary alpha-linolenic acid induced some modifications of the levels of endogenous dopaminergic neurotransmitters in all brain areas but was related to a very low incorporation of trans polyunsaturated fatty acids. Increasing the dietary levels of cis alpha-linolenic acid succeeded in correcting the endogenous neurotransmitter concentrations only in the frontal cortex but not in the striatum and the hippocampus. Thus, the levels of dopamine were lowered by 95% in the hippocampus. These results suggest that in addition to the imbalance generated by their presence, trans fatty acids may directly act on the concentration of dopaminergic neurotransmitters.