The pyrogen standard of the Pharmacopoeia of the German Democratic Republic--which is recommended in the Compendium Medicamentorum and the Pharmacopoeia of the CMEA countries, consists of a selected batch of sodium nucleinate, the pyrogenicity of which had been demonstrated in very many rabbits. One ampoule of this standard contains 10 mg freeze-dried sodium nucleinate. After inoculation of 0.4 mg per kg of body weight into rabbits an increase in temperature of 0.8 degrees C or more will occur. Westphal assumes that the reason for the pyrogenicity of sodium nucleinate is possibly due to its obligatory contamination with bacterial lipopolysaccharides. Some investigations to find out if the properties and effects of this standard are different from those of isolated bacterial lipopolysaccharides have been performed by the author: adsorption by plastic granulates, inactivation by heating and by incubation with horse serum, temperature changes produced by inoculation into rabbits and results of investigations using the limulus amebocyte lysate test. The results of the investigations did not show significant differences between sodium nucleinate and isolated bacterial lipopolysaccharides. This is in agreement with Westphal's hypothesis mentioned above.