Patients with sepsis often manifest symptoms of encephalopathy similar to those observed in portasystemic encephalopathy. As a causal relationship has been demonstrated between hepatic encephalopathy and a deranged brain neurotransmitter profile, the catecholaminergic and serotoninergic brain neurotransmitter profile in a septic rat model was investigated. Septic animals exhibited lower levels of norepinephrine (NE), 3,4-dihydroxyphenylacetic acid, and homovanillic acid compared to normal controls. Severely septic animals with encephalopathy exhibited significantly lower levels of NE, dopamine, 5-hydroxytryptamine, and 5-hydroxyindoleacetic acid compared to rats only mildly septic with no encephalopathy. The infusion of branched chain amino acids during sepsis had no effect on this deranged brain neurotransmitter profile. Previous results of derangements in the blood-brain barrier transport mechanism combined with the present findings of a deranged brain amino acid and neurotransmitter profile during sepsis may be responsible, at least in part, for the metabolic encephalopathy observed during sepsis and might suggest a common etiology for septic, hepatic, and other metabolic encephalopathies.