Reversal of chronic hepatic encephalopathy by colonic exclusion: poor correlation with blood GABA levels. Previous studies have suggested that the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) is a key factor in the syndrome of portasystemic encephalopathy. We report the case of a patient with medically intractable portasytemic encephalopathy after portacaval shunt who had marked clinical improvement after creation of an end ileostomy. Plasma GABA and serum ammonia levels were measured before and after ileostomy. Although the clinical syndrome and the EEG improved markedly after the ileostomy, the plasma GABA levels remained markedly elevated. Preoperative and postoperative GABA levels were 865 and 633 pmol/ml, respectively (nl = 100-180 pmol/ml). Our findings confirm previous reports of the efficacy of colonic exclusion in patients with intractable portasystemic encephalopathy. However, our results conflict with the hypothesis that GABA itself is the key mediator of the syndrome. 