To investigate the selectivity of serum immunoreactive prolyl 4-hydroxylase (S-IRPH) as a marker for hepatic necrosis, sera were taken from patients with hepatic inflammation and hepatic necrosis. The concentration of immunoreactive prolyl 4-hydroxylase in the sera was determined by radio-immunoassay, and S-IRPH and alanine aminotransferase (ALT) data were plotted. Patients with hepatic necrosis showed mainly prolyl 4-hydroxylase elevation while patients with inflammation had both prolyl 4-hydroxylase and alanine aminotransferase elevations. The addition of serum immunoreactive prolyl 4-hydroxylase to current serum markers would be useful in investigating the pathophysiology of hepatocellular damage, particularly in differentiating between hepatic necrosis and inflammation.