The physical properties of cell membranes play an important role in cellular homeostasis. Previous studies with animal models have shown that the hepatocyte membrane fluidity has important effects in cellular function. In order to further investigate the relationship between physical properties of membranes and liver disease, the present study was performed. Twenty-nine patients with different degrees of liver injury and 10 control individuals were studied. A lower membrane fluidity--as assessed by diphenylhexatriene fluorescence polarization--was observed in membrane preparations from patients, as compared to controls. These alterations are positively correlated with the severity of liver damage and could be accounted for by a higher cholesterol content of patients' membrane preparations.