Serum lipids, lipoproteins, cholesterol absorption and parameters of cholesterol metabolism were related to apolipoprotein E phenotypes in 38 patients with familial xanthomatous hypercholesterolemia. Serum lipids and lipoproteins were similar in 2 most frequent apo E phenotypes E 3/3 and E 4/3. Coronary artery disease was not related to the apo E phenotypes. Cholesterol absorption efficiency was significantly lower in the apo E 3/3 patients than in the apo E 4/3 group. A high serum level of cholesterol precursor lathosterol, a high lathosterol/sitosterol ratio and sterol balance data suggest that cholesterol synthesis may be slightly higher in the apo E 3/3 than E 4/3 group. The findings indicate that the genetically determined apo E polymorphism contributes to cholesterol absorption efficiency in FH patients, but serum total and lipoprotein cholesterol levels are poorly related to apo E isoforms.