1. The concentrations of four serum glycoproteins, thyroxine-binding globulin, α 2 -macroglobulin, α 1 -antitrypsin and transferrin, as well as their reactivities with concanavalin A and lentil-lectin, were measured in patients with hepatocellular carcinoma or fulminant hepatic failure and in normal subjects. 2. Serum concentrations of thyroxine-binding globulin and α 1 -antitrypsin were significantly greater in patients with hepatocellular carcinoma than in normal subjects, and the percentage lentil-lectin reactivity of these two proteins was markedly increased. 3. With the exception of transferrin, which did not bind to lentil-lectin, an enhancement of lentil-lectin reactivity was observed for the glycoproteins in serum from patients with fulminant hepatic failure. No difference in concanavalin A binding was found between the groups for any of the glycoproteins. 4. Altered fucosylation, as indicated by increased lentil-lectin binding, occurs in several glycoproteins arising in malignant and non-malignant conditions associated with abnormal hepatic regeneration.