Serum β2-microglobulin (β2μ) was determined in 44 patients with primary biliary cirrhosis (PBC) and in 63 patients with other liver disorders. β2μ levels were elevated in PBC when compared with chronic persistent hepatitis, primary sclerosing cholangitis and noncirrhotic alcohol liver disease, but not in comparison with chronic active hepatitis and alcoholic liver cirrhosis. With the exception of chronic persistent hepatitis, all liver disorders had significantly increased serum concentrations of β2μ when compared with controls. A significant correlation between β2μ and erythrocyte sedimentation rate (p < 0.001) and β2μ and serum IgG (p < 0.05) was found in PBC. No significant difference in β2μ levels was noted when PBC patients with early and late histopathological changes were compared. D-penicillamine treatment significantly (p < 0.01) but transiently reduced β2μ levels in PBC; this may reflect the presumed immunosuppressive action of this drug.