In order to characterize the abnormalities of the lipoprotein profile in familial hypercholesterolemia (FH), serum apolipoprotein AI, AII, B, CII, CIII, and E levels were determined by the turbidimetric immunoassay in 48 patients with heterozygous FH. Apolipoprotein B levels in FH were about 2.5 fold higher (203 +/- 48 mg/dl, mean +/- S.D.) than the 30 age-matched normolipidemic control subjects (84 +/- 13 mg/dl). Significant increments of apolipoprotein CII, CIII, and E levels were observed in FH (4.6 +/- 1.6, 11.0 +/- 3.6 and 6.4 +/- 1.7 mg/dl, respectively) as compared with those in normal subjects (3.0 +/- 0.9, 7.7 +/- 1.6 and 4.5 +/- 1.1 mg/dl, respectively). Apolipoprotein AI and AII levels in FH were 130 +/- 27 and 32 +/- 6.0 mg/dl, respectively, which were not significantly different from the levels in normal subjects (131 +/- 18 and 31 +/- 5.4 mg/dl, respectively). The ratio of low density lipoprotein (LDL) cholesterol to apolipoprotein B was significantly higher in FH (1.3 +/- 0.3) than that in normal subjects (1.2 +/- 0.1). This indicates that the LDL of FH was cholesterol-rich in comparison with that of normal subjects. The ratio of high density lipoprotein (HDL) cholesterol to apolipoprotein AI in FH (0.34 +/- 0.07) was significantly lower than that in normal subjects (0.39 +/- 0.05). This difference might possibly be produced by an abnormal HDL metabolism of FH patients, a topic which remains to be elucidated by further investigation.