Solutions containing bacterial lipopolysaccharides (P) and sodium nucleinate (NN) solutions filtered through cellulose asbestos filters became pyrogen free. But the filters, with respect to the pyrogenicity of these solutions, became earlier exhausted in case of NN than in case of P. A 12-min heating to 121 degrees C in the autoclave led to a significant lowering of pyrogenicity both in P- and in NN-solutions. After a 2-h heating in same conditions both P- and NN-solutions in the chosen ranges of concentration became pyrogen free.