When studying disorders fat metabolism in respect to ischemic heart disease great attention has been recently paid first of all to the protein component of lipoprotein complexes, apolipoproteins. Apolipoproteins seem to be much more sensitive indicators of coronary atherosclerosis risk than so far commonly used "lipid" ones. In the presented study we introduce our experience concerning apolipoprotein B assessment by means of rocket technique using foreign made antisera in comparison with antiserum of the Czechoslovak production made by USOL Prague. Our results are comparable with those of foreign and Czechoslovak authors who assessed apolipoprotein B by technically more demanding methods. When using antisera USOL and Behring the established values of apolipoprotein B are comparable both in patients in whom fat metabolism disorder was not proved and in patients with familial hypercholesterolaemia in whom the values of apolipoprotein B are the highest. Indications of apolipoprotein B investigation and its significance for clinical practice are discussed.