In comparison with healthy persons, chronic uremic patients on regular hemodialysis treatment had significantly higher blood serum concentrations of α1-acid glycoprotein, ceruloplasmin and C4 complement component, while levels of haptoglobin, C3 and transferrin were lower. Serum α2-macroglobulin and α1-antitrypsin levels were similar in both groups. Hemodialysis with cuprophan membrane induced only slight changes in some of these glycoproteins during a 48-hour follow-up period. Seven hours after termination of hemodialysis slight, but significant, decreases in blood serum transferrin and α1-antitrypsin concentrations were observed. Hemodialysis thus does not seem to induce a conspicuous acute-phase reaction.