In 26 patients with chronic liver disease, the serum viscosity was studied. In 42% of subjects, the serum viscosity was found increased, almost always associated with clinical findings of central nervous system involvement. The remission of central nervous system symptoms occurs with fall into normal range of serum viscosity levels. Therefore, the serum hyperviscosity should be included among various causes of cirrhosis encephalopathy. When serum viscosity is increased, relates rather to immunoglobulins (IgG, IgA, IgM) increases then to increased amounts of total globulins.