Serum samples from 20 patients with acute exacerbation of chronic hepatitis due to hepatitis B virus and 20 patients with hepatocellular carcinoma arising from B viral cirrhosis with elevated levels of alpha-fetoprotein (AFP) were analyzed by affinity column chromatography for concanavalin A binding. Serum AFP was tested at regular intervals in all of these patients. Acute exacerbation was defined as elevation of serum transaminase greater than 300 IU/L in patients with chronic hepatitis B. In hepatocellular carcinoma, serum AFP levels fluctuated but remained higher than 92 ng/ml, whereas, in acute exacerbation of chronic hepatitis B, serum AFP levels returned to normal within 3-12 months of follow-up. The results of concanavalin A-binding assay revealed that AFP from both these groups had a high affinity for concanavalin A, and this assay could not be used to discriminate between the two conditions.