An aim of the investigation was to prepare bioactive compounds from components of natural food or convertible ones to useful and harmless material by degradation. Particularly, some heterocyclic compounds derived from amino acids and peptidcs, guanidinopyrimidines, pseudopurines, dithianethiones, isocoumarins were considered as the object. On the whole, about 500 compounds were newly prepared and examined on their biological activities. As for carbohydrates, oxidation with periodate, preparation of amino acid derivatives from oxidized polysaccharides, preparation of nitro- and amino-polysaccharides, synthesis of triazine derivatives from polysaccharides etc. some investigations on chemical modifications of polysaccharides were made. The oxidation by periodate was also applied to proteins, especially some enzymes. By the oxidation, certain relationship between constitution and biological activity, expressly a role of tryptophan, was elucidated. Two allergenic substances were isolated from liver flukes and their constitutions were clarified. The allergenic principle was an RNA linked with a small peptide. Starting from the idea of RNA-complex, a preparation of an RNA fraction from tumor cells, a complex formation of the RNA with basic polymers, and an attenuation of tumor cells by treating with the complex were described. Furthermore, by inoculating beforehand with the attenuated tumor cells, the transplantation of tumor and thereby challenge inoculation were inhibited completely. Moreover, analyses, separations, decompositions and other subjects as to some natural products were mentioned briefly.