1. We have shown that serum total sialic acid is elevated in hypertriglyceridaemic patients showing the Frederickson's type IIB phenotype in comparison with normal subjects (2.30 ±0.34 versus 1.92 ± 0.32 mmol/l, P <0.02). Lipid-associated sialic acid was also elevated in the hypertriglyceridaemic group in comparison with the normal subjects (0.60 ±0.09 versus 0.35 ±0.04 mmol/l, P <0.001). 2. We measured five serum acute-phase proteins in the hypertriglyceridaemic patients and the normal subjects, namely α 1 -antichymotrypsin, α 1 -acid glycoprotein, α 2 -macroglobulin, C-reactive protein and haptoglobin. Serum α 2 -macroglobulin was significantly elevated in the hypertriglyceridaemic patients compared with the normal subjects (2.1 ±1.0 versus 1.5 ± 0.55 g/l, P <0.05) as was serum C-reactive protein (5.9 ±3.5 versus 3.5±1.9mg/l, P <0.05). There were, however, no significant differences in the serum concentrations of α 1 -antichymotrypsin, α 1 -acid glycoprotein or haptoglobin between the two groups. 3. There was a significant correlation between serum total sialic acid and serum α 1 -antichymotrypsin, α 1 -acid glycoprotein and haptoglobin (Spearman correlation coefficients 0.74, 0.50 and 0.76, respectively) in the normal subjects, and there was a significant correlation between serum total sialic acid and serum α 1 -antichymotrypsin and α 1 -acid glycoprotein (Spearman correlation coefficients 0.72 and 0.84, respectively) in the hypertriglyceridaemic patients.