Surface substances of the bacterial cell which would have biological and immunological activities were studied with aid of purification process, chemical analysis, spectrochemical procedures, viscosimetory, dielectric spectrometory, osmotic manometory and other physicochemical procedures. Purified substance from Gram positive bacterial cell by trichlor-acetic acid method was determined to be the mixture of ribonucleic acid-Mg and polysaccharde-polypeptide-lipid. Mixture was consisted of ion-binding in one-fifth and its molecular weight was ca. 400,000 with axis ratio of 1:2. By acting with ribonuclease this mixture was purified into polysaccharide-polypeptide-lipid compound which, to date, had been difficult to purify from Gram positive bacterial cell. Purified polysaccharide-polypeptide-lipid compound from Gram negative bacterial cell using trichlor-acetic acid method was also studies revealing molecular weight of ca. 150,000 and twice longer axis ratio than ribonucleic acid mixture. Thus, it was considered that parallel coexistence of two molecules of ribonucleic acid-Mg and one molecule of polysaccharide polypeptide-lipid compound was clarified. Polysacchardie-polypeptide-lipid compound was further purified into polysaccharide-polypeptide 1 (PP 1), polysaccharide-polypeptide 11 (PP 11) and lipid. From measuring molecular weight, km constant, axis ratio etc, it was found that PP 1 had more elongated molecular form than PP 11 and that relationship between PP 1 and PP 11 was identical with that between non-denaturated protein and denaturated protein.