Lipoproteins are water-soluble complexes through which fats and lipids are transported between the various tissues for storage and utilization. Association of lipoproteins with risk of coronary heart disease and various types of dyslipoproteinemias necessitate the quantification of the individual lipoprotein classes. One of the most commonly used techniques for the separation of ß and pre- ß lipoproteins is the precipitation technique. However, none of the lipoprotein separation techniques used in laboratories has been developed for use in animal lipoproteins. It was suggested that lipoprotein separation preocedures might require modification before they are applied to the plasma of a given animal species. Therefore, the present study was undertaken to compare the concentrations of heparin/MnCl₂ necessary in order to precipitate ß + pre- ß lipoproteins of human and various animal sera. The lipoproteins precipitated were separated and identified by agarose gel electrophoresis. In accordance with the original heparin/MnCl2 precipitation method being commonly used for human serum, 200 IU heparin / 46 µ mol MnCl₂ yielded complete precipitation of ß + pre- ß lipoproteins in sera from all the animal species investigated except bovine and chicken. Bovine serum required approx. 2 times more heparin/MnCl₂ for the precipitation of these lipoprotein classes whereas chicken serum required half of the reagent concentration as compared to human serum. However, complete dissociation and electrophoretic separation of the precipitated lipoproteins by the heparin/MnCl₂ method were not achieved. It was concluded therefore that the concentrations of polyanion/divalent cation used for the precipitations of serum ß + pre- ß lipoproteins differ between human and several animal species. The existing differences might be attributed to the variations in charge densities of lipoproteins’ surface as well as to dissimilarities in lipid compositions of the lipoproteins among species.