A comparative study of urinary excretion of octopamine, dopamine, and noradrenaline catabolic products, respectively parahydroxymandelic acid (PHMA) homovanillic acid (HVA) and vanylmandelic acid (VMA) was carried out in 27 cirrhotic patients with (11) and without (16) porto-systemic encephalopathy (P.S.E). PHMA, HVA and VMA were significantly higher in patients with PSE, and there was a positive correlation between PHMA and HVA, and between PHMA and VMA. Higher excretion of PHMA in patients with PSE strongly suggests an increased metabolism of octopamine. HVA and VMA increased excretion, and the positive correlations could be explained by the depletion of stored dopamine and noradrenaline. These observations support the hypothesis that octopamine acts as a false neurotransmitter, and the resulting depletion of dopamine and noradrenaline could explain the neuropsychic phenomena of PSE, and the awakening effect of L. Dopa treatment.