Abstract Cholesterol and triglycéride content of serum lipoprotein fractions isolated by ultracentrifugation have been studied in 33 healthy subjects and in 56 subjects affected by hyperlipoproteinemia of type IIa, IIb and IV. Patients with atherosclerotic disease were characterized by a general decrease of HDL cholesterol and by a negative correlation between HDL cholesterol and VLDL triglycerides; patients with type IIb and IV showed an increase of LDL lipoproteins. The increase of triglycerides in type IIb and IV was caused by elevation of VLDL triglycerides or LDL triglycerides, and the increase of cholesterol in type IIb is sometimes caused by elevation of VLDL cholesterol. It is evident that several subtypes exist within Fredrickson's classification. Patients with cerebral arterial disease when compared with patients affected by non-ischaemic disease, showed a negative and significant correlation between HDL cholesterol and total cholesterol.