A. L. Mndzhoyan, the director of the Institute of Fine Organic Chemicals of the Academy of Sciences of the Armenian SSR, pointed out In his opening address the urgency of the work on the structure modification of natural compounds with the aim of creating medicinal preparations and elucidating the relationships between chemical structure and biological activity and emphasized the importance and promise of a new trend, the microbiological modification of the structure of natural, physiologically active compounds. One of the principal problems of the symposium was the modification of the structure of antibiotics, dealt with in review reports by Corresponding Member of the Academy of Sciences of the USSR A. S. Khokhlov, and Member of the Academy of Sciences of the Armenian SSR Academician A. L. Mndzhoyan. A.S. Khokhlov discussed the current state of the problem of producing and studying modified antibiotics and summed up the work of modernization of known antibiotics. The analysis of this work enabled the author to derive certain general inferences concerning the further trends and organization of the research on modification of antibiotics. A. L. Mndzhoyan reported on the development of research in the field of natural and semisynthetic penicillins and the reasons for the unabated interest in these antibiotics. The author summed up the extensive research in the field of semisynthetic penicillins, carried out at the Institute of Fine Organic Chemicals, Academy of Sciences of the Armenian SSR, and reported the data obtained at the institute on the dependence of the biological properties of the new penicillins on the structure and composition of individual functional groups and the general structure of the compounds. Interesting data on the synthesis, research, and properties of semisynthetie penicillins which are derivatives of furane, 5-nitrofurane, ~/-butyrolactone, and doubly substituted acetic acid, containing (~naphthyl residues, were reported by T. A. Veinberg (Institute of Organic Synthesis, Academy of Sciences of the Lithuanian SSR), Yu. Z. Ter-Zakharyan (ITOKh), T. N. Rozanova (All-Union Antibiotics Research Institute, VNIIA), and Sh. G. Oganyan (institute of Fine Organic Chemistry, ITOKh). A report of E. N. Lazareva (VNIIA) dealt with the problems of prolonging the action of the antibiotics in the organism and the chemical modification of chlortetracycline, tetracycline, oxytetracycline, streptomycin, and dihydrostreptomycin. It was shown that it is possible, in principle, to obtain analogs of dihydroInstitute of Fine Organic Chemicals, Academy of Sciences of the Armenian SSR, Erevan. Translated