A method for quantitating a specific component in lipoproteins contained in a biological sample, for example, HDL (high-density lipoprotein), LDL (low-density lipoprotein) or VLDL (very low-density lipoprotein) by using a commonly employed automatic analyzer without centrifuging or making the reaction liquor cloudy due to complexes or aggregates. Namely, a controlling means, whereby an enzyme reaction can be carried out exclusively for the target component, is introduced into a method for enzymatically assaying a component in a specific lipoprotein fraction in the serum, thereby specifically assaying the component.