Six acute phase proteins (haptoglobin, alpha 1-acid glycoprotein, alpha 1-antitrypsin, alpha 2-macroglobulin, C reactive protein and transferrin) have been measured in the sera of chronic liver disease (CLD) patients with different aetiology (viral, autoimmune and alcoholic) and histology (steatosis, chronic persistent hepatitis, chronic active hepatitis, cirrhosis), and in patients with liver cancer. 1) The most striking changes concerned alpha 2-macroglobulin (increased) and haptoglobin (decreased) levels. 2) Transferrin was lower in alcoholic liver disease than in viral CLD, CRP was lower in autoimmune than in viral or alcoholic CLD, and alpha 1-acid glycoprotein was lower in viral and alcoholic CLD than in autoimmune CLD. Acute phase protein assay may prove useful in differential diagnosis, particularly when specific markers are not available (autoimmune, non A, non B, alcoholic liver diseases). 3) No significant differences related to aetiology (B, non A non B, D viruses) were observed in viral CLD. 4) Patients who progressed to CLD after acute viral hepatitis type B or non A non B did not show different APP levels from those who had recovered when tested 8-12 months after the acute phase. 5) The pattern of APP changes observed in primary liver cell carcinoma was different from both the cirrhotic pattern and the pattern presented by other tumours with or without liver metastasis.