The copper concentration in the lysosomes of periportal hepatocytes of nine patients with primary biliary cirrhosis was determined by X-ray microanalysis in ultrathin sections, the chlorine concentration of the embedding medium being taken as internal standard. A positive correlation was found between the lysosomal and the total liver copper concentration. No correlation was found between the lysosomal copper concentration and the grade of orcein staining for lysosomal copper-associated protein in paraffin sections. It is concluded that in contrast to the grade of orcein staining, the lysosomal copper concentration is a reliable measure of the total liver copper concentration in primary biliary cirrhosis.