Microheterogeneity of transferrin (Tf) with concanavalin A (ConA) affinity was investigated by sensitive lectin-affinity electrophoresis and antibody-affinity blotting technique of sera obtained from patients with alcoholic liver disease (ALD) and normal subjects. Serum Tf was separated by ConA into three bands-a strongly ConA-reactive major band (C1), a weakly reactive minor band (C2), and a non-reactive trace band (C3). The C3 fraction was significantly increased in patients with ALD before alcohol abstinence, compared with normal subjects and patients with ALD after 4 weeks of abstinence. Furthermore, a significant correlation was found between the C3 fraction and serum carbohydrate-deficient transferrin or gamma-glutamyl-transpeptidase. These results indicate that the microheterogeneity of serum Tf in patients with ALD may be a more complex abnormality of elongation and processing on the glycans than merely a loss of terminal sialic acids. Determination of the C3 fraction is a useful marker for ALD.