Using the RELP analysis we studied the frequency of X2 allele of apoB gene in three groups of patients: 1) men at the age of 20-59 with lipid metabolism disorders revealed in population inspection of Oktyabrsky district in Moscow; 2) men with ischaemic heart disease and 3) healthy men. It was established that in individuals suffering from type IIa hyperlipidemia the frequency of X2 allele was significantly higher than in healthy donors from Moscow population. Homozygotes for X2 allele of XbaI RELP had 7-9% higher serum cholesterol levels, than homozygotes for X1 allele. The study suggests the X2 allele of the apoB gene to be associated with the development of high plasma cholesterol level. No significant difference in X2 allele frequencies was found between patients with ischaemic heart disease and healthy donors. There was also no association found between cholesterol and triglyceride levels and the presence of X2 allele in this group of patients.