The concentration of adenosine 3':5'-cyclic monophosphate in the spinal fluid of ten patients with liver dysfunction was analyzed. Ages of the patients ranged from 31 to 75 years. The state of consciousness varied between normality and stupor. After a liver biopsy the diagnoses were as follows: cirrhosis in six cases, porphyria cutanea tarda in one case, hepatic metastases in two cases and Wilson's disease in one case. Mean values in these patients (22.91 +/- 4.18 pM/ml) have been significantly greater (p less than 0.0005) than those in ten control individuals (15.55n control individuals (15.44 +/- 3.66 pM/ml). Values corresponding to two patients in coma were still higher (52.62 and 36.50 pM/ml respectively). A previous lumbar puncture carried out in one of these patients when he was conscious showed a figure of 23 pM/ml. These results suggest a progressive rise of cyclic adenosine monophosphate in the spinal fluid in relation to clinical impairment, and may indicate a similar behaviour for this nucleotide to that of tryptophan, as reported by other authors. These findings point toward the role of the alteration of neurotransmitters in the pathogenesis of hepatic coma.