Localization of two phospholipid haptens--cardiolipin and phosphatidylinositol--in mouse liver sections was studied by the indirect method of fluorescent antibodies. Two types of liver sections--paraffin and cryostat, and two type of fixation--in acetone, and in the acetone, buffer, and formalin mixture--were used. Antiphospholipid sera stain specifically the plasma membrane of hepatocytes and predominantly the membrane region overlooking the blood capillary. A possibility of detecting the specific phospholipid haptens depends on the method of obtaining the sections and their fixation. Two types of immunization give two types of antiphospholipid sera which differ by the stability, by the possibility of monospecific antibodies isolation from them on lipid immunosorbents, and by the types of liver section staining.