During the five last years, we observed under the microscope all the hyperlipidemic sera received in our laboratory, to search a lipid particle agglutination. We have retained 24 sera with obvious agglutination (9 types V, 9 types IV and 6 types IIb), the lipidemia of which was compared, type to type, to 56 control sera (16 types V, 16 types IV and 24 types IIb), in which no agglutination has been found. We observed significant differences in the means of cholesterol (CT) triglycerids (TG), vitamin A (VA) and CT/TG, VA/TG and VA/CT ratios, comparing agglutinated and control sera. These differences suggest that the agglutination phenomenon is in relation with the nature of the lipid particles present in the hyperlipidemic sera, which could be "chylomicron remnants" in type V hyperlipidemias, and other forms of "remnants" in type IV and IIb hyperlipidemias. These "remnants" could result from a blockade of lipolysis. This blockade of lipolysis in the agglutinated sera might be related to what is known about the authentificated autoimmune hyperlipidemia (AIH). Thus we can suppose that hyperlipidemias with obvious serum lipid particle agglutination are autoimmune hyperlipidemias.