Automated analysis of aromatic and branched chain amino acids was performed in plasma and in four cerebral regions of rats submitted to chronic porto-caval shunt. Compared to controls, plasma of the operated animals exhibited a significant diminution of valine, leucine, isoleucine, a net increase of phenylalanine and tyrosine, with unchanged tryptophan levels. Brain valine, leucine and isoleucine were either increased or unchanged, whereas an enormous increase of aromatic amino acids, uniform in the four cerebral regions, was observed. The lack of correlation between plasmatic and cerebral levels of these essential amino acids leads to the hypothesis that cerebral permeability to amino acids is modified after experimental portocaval anatomosis: we recent confirmed that blood-brain mediated transport of the neutral amino acids is increased in this condition. A slower cerebral turnover of these metabolites could also contribute to elevate their cerebral concentrations after portocaval shunt.