The prevalence of liver damage in patients receiving long-term anticonvulsant therapy was determined, using a new marker of liver disease, the serum F protein concentration. Abnormal serum F protein concentrations were detected in 50 per cent of 34 patients receiving anticonvulsant therapy. A retrospective analysis of post-mortem liver samples showed common histological abnormalities in three out of seven patients who had died whilst receiving anticonvulsant therapy. These changes were not seen in control patients. We suggest that chronic anticonvulsant therapy may cause significant hepatocellular damage.